Multi-user parallel channel access in WLAN systems

ABSTRACT

A method and apparatus may provide multi-user parallel channel access (MU-PCA) and/or single-user parallel channel access (SU-PCA) using transmit and/or receive with symmetrical bandwidth, in the downlink (DL), uplink (UL), or combined DL and UL. SU-PCA and MU-PCA may support unequal modulation and coding schemes (MCS) and unequal transmit power. Medium access control (MAC) layer, Physical layer (PHY), and mixed and PHY layer methods and procedures may support UL, DL and combined UL and DL SU-PCA and MU-PCA using transmit and/or receive with symmetrical bandwidth. MU-PCA and/or SU-PCA may also be supported by MAC and PHY layer designs and procedures for downlink, uplink and combined uplink and downlink using transmit/receive with asymmetrical bandwidth.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/605,538, filed Mar. 1, 2012, and U.S. Provisional Application No.61/669,505, filed Jul. 9, 2012, and U.S. Provisional Application No.61/684,051, filed Aug. 16, 2012, the contents of which are herebyincorporated by reference herein.

BACKGROUND

A Wireless Local Area Network (WLAN) in Infrastructure Basic Service Set(BSS) mode may have an Access Point (AP) for the BSS and one or morestations (STAs) associated with the AP. The AP may have access orinterface to a Distribution System (DS) or another type ofwired/wireless network that carries traffic in and out of the BSS.Traffic to STAs that originates from outside the BSS may arrive throughthe AP and may be delivered to the STAs. Traffic originating from STAsto destinations outside the BSS may be sent to the AP to be delivered tothe respective destinations. Traffic between STAs within the BSS mayalso be sent through the AP where the source STA may send traffic to theAP and the AP may deliver the traffic to the destination STA. Suchtraffic between STAs within a BSS may be considered peer-to-peertraffic. Such peer-to-peer traffic may also be sent directly between thesource and destination STAs with a direct link setup (DLS) using, forexample, an 802.11e DLS or an 802.11z tunneled DLS (TDLS). A WLAN inIndependent BSS (IBSS) mode may have no AP and STAs may communicatedirectly with each other. This mode of communication may be referred toas “ad-hoc” mode of communication.

In an 802.11 infrastructure mode of operation, the AP may transmit abeacon on a fixed channel called primary channel. This channel is 20Mega-Hertz (MHz) wide and is the operating channel of the BSS. Thischannel is also used by the STAs to establish a connection with the AP.The fundamental channel access mechanism in an 802.11 system is CarrierSense Multiple Access with Collision Avoidance (CSMA/CA). In this modeof operation, every STA, including the AP, may sense the primarychannel. If the channel is detected to be busy, the STA may back off.Hence, only one STA may transmit at any given time in a given BSS.

In 802.11n, High Throughput (HT) STAs may also use 40 MHz wide channelfor communication. This may achieved by combining the primary 20 MHzchannel with another adjacent 20 MHz channel to form a 40 MHz widechannel. In 802.11ac, Very High Throughput (VHT) STAs may support 40MHz, 80 MHz and 160 MHz wide channels. While 40 MHz and 80 MHz channelsmay be formed by combining contiguous 20 MHz channels similar to 802.11nabove, 160 MHz channel may be formed either by combining 8 contiguous 20MHz channels or two non-contiguous 80 MHz channels (80+80configuration). In case of “80+80” configuration, the data, afterchannel encoding, may be passed through a segment parser that may divideit into two streams. Inverse Fast Fourier Transform (IFFT) and timedomain processing may be done on each stream separately. The streams maythen be mapped on to the two channels and the data may be sent out. Onthe receiving end, this mechanism may be reversed and the combined datamay be sent to the medium access control (MAC) layer.

In sub 1 GHz modes of operation (for example, 802.11af and 802.11ah),the channel operating bandwidths may be reduced when compared to 802.11nand 802.11ac. 802.11af may support 5 MHz, 10 MHz and 20 MHz wide bandsin TV White Space (TVWS) while 802.11ah may support=1 MHz, 2 MHz, 4 MHzand 8 MHz in non-TVWS. Some STAs in 802.11ah may be considered to besensors with limited capabilities and may only support 1 MHztransmission mode.

In WLAN systems with multiple channel width such as 802.11n, 802.11ac,802.11af and 802.11ah, there may be a primary channel, which may have abandwidth equal to the largest common operating bandwidth supported byall STAs in the BSS. The bandwidth of the primary channel may be limitedby the STA that supports the smallest bandwidth operating mode. In theexample of 802.11ah, the primary channel may be 1 MHz wide if there areSTAs that only supports 1 MHz mode while the AP and other STAs in theBSS may support 2 MHz, 4 MHz, 8 MHz and 16 MHz operating modes. Allcarrier sensing and NAV setting may depend on the status on the primarychannel. For example, if the primary channel is busy, due to an STAsupporting only 1 MHz operating mode transmitting to the AP, then theentire available frequency bands may be considered busy even though themajority of it may be idle and available. In 802.11ah and 802.11af, allpackets may be transmitted using a clock that may be down clocked 4 or10 times as compared to the 802.11ac specification.

In the United States, the available frequency bands which may be used by802.11ah may be from 902 MHz to 928 MHz; in Korea, from 917.5 MHz to923.5 MHz; and in Japan, from 916.5 MHz to 927.5 MHz. The totalbandwidth available for 802.11ah may be 6 MHz to 26 MHz depending on thecountry code.

In addition, in the 802.11 Standards, only one STA may be able totransmit at any given time in a BSS. On the DL (i.e. where the APtransmits to a STA), if Multi-User multiple-input multiple output(MU-MIMO) is not used, the AP may conduct packet exchanges with only oneSTA at any given time. If multi-user MIMO (MU-MIMO) is utilized, the APmay transmit to multiple STAs. However, all STAs involved in MU-MIMO maybe communicating on the same band, which may be limited by the STAs withthe smallest operating bandwidth. In this scenario, remaining frequencybandwidth may remain idle even though it may be available to the AP andother STAs.

SUMMARY

A method and apparatus may provide multi-user parallel channel access(MU-PCA) and/or single-user parallel channel access (SU-PCA) usingtransmit and/or receive with symmetrical bandwidth, in the downlink(DL), uplink (UL), or combined DL and UL. SU-PCA and MU-PCA may supportunequal modulation and coding schemes (MCS) and unequal transmit power.Medium access control (MAC) layer, Physical layer (PHY), and mixed andPHY layer methods and procedures may support UL, DL and combined UL andDL SU-PCA and MU-PCA using transmit and/or receive with symmetricalbandwidth. MU-PCA and/or SU-PCA may also be supported by MAC and PHYlayer designs and procedures for downlink, uplink and combined uplinkand downlink using transmit/receive with asymmetrical bandwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2A shows an example of a WLAN BSS including an AP and four STAs;

FIG. 2B shows an example of frequency resource wastage in a WLAN systemwith multiple channel widths;

FIG. 3 shows an example frame format for a group request-to-send (G-RTS)control frame;

FIG. 4 shows an example frame format for a group clear-to-send (G-CTS)control frame;

FIG. 5 shows an example frame format for a multi-user parallel channelaccess (MU-PCA) management (MPM) frame;

FIG. 6 shows an example medium access control (MAC) scheme for enablingDL MU-PCA using control frames over multiple channels;

FIG. 7 shows an example MAC scheme for standalone downlink (DL) MU-PCAusing G-RTS and G-CTS on the primary channel;

FIG. 8 shows an example MAC scheme for enabling DL MU-PCA using controlframes over multiple channels, and which also enables MU-PCA for WiFiSTAs;

FIG. 9 shows an example MAC scheme for enabling DL MU-PCA using controlframes and block acknowledgments (BAs);

FIG. 10 shows an example frame format of the Uplink Request frame (ULR);

FIG. 11 shows an example frame format of the Group-Poll (G-Poll) frame;

FIG. 12 shows an example MAC scheme supporting uplink (UL) MU-PCA fordata without strict delay bound;

FIG. 13 shows an example MAC scheme supporting UL MU-PCA for data withstrict delay bound;

FIG. 14 shows an example MAC scheme supporting UL MU-PCA for data wherethe ULR packets are transmitted sequentially;

FIG. 15 shows an example MAC scheme supporting UL MU-PCA for data withmixed delay requirements;

FIG. 16 shows an example of a MAC scheme supporting the combined DL andUL MU-PCA;

FIG. 17 shows an example flow diagram of a method for combined DL and ULMU-PCA performed by a STA in a BSS system;

FIG. 18 shows an example MAC scheme supporting the combined UL and DLMU-PCA;

FIG. 19 shows an example MAC scheme where the UL MU-PCA transmission areinitiated by ULR transmitted sequentially on the primary channel;

FIG. 20 shows an example MAC scheme enabling combined DL/UL MU-PCA usingcontrol frames over multiple channels and which also enables MU-PCA forlegacy WiFi STAs;

FIG. 21 shows an example transmission flow diagram with a user capableof channel aggregation;

FIG. 22 shows an example physical (PHY) layer scheme with physical layerconvergence protocol (PLCP) headers transmitted on separate frequencychannels;

FIG. 23 shows an example of DL transmission flow diagram at an AP overhybrid aggregated channels;

FIG. 24 shows an example flow of PLCP protocol data unit (PPDU)transmissions over channels including hybrid aggregated channels;

FIG. 25 shows another example flow of PPDU transmissions over channelsincluding hybrid aggregated channels;

FIG. 26 is a flow diagram of an example method of using layer mapping tomay N MAC packets to K layers;

FIG. 27 shows an example of a PHY layer scheme with 3 MU-PCA users;

FIG. 28 shows an example of a PHY layer scheme with 2 MU-PCA users;

FIG. 29 shows an example of a PHY layer scheme with an example STFformat for MU-PCA transmissions;

FIG. 30 shows an example PHY layer scheme with PPDUs using longpreamble;

FIG. 31 shows an example transmission flow diagram for transmitting DLcommunications;

FIG. 32 shows an example transmission flow diagram for transmitting ULcommunications;

FIG. 33 shows an example transmission flow diagram for receiving ULcommunications; and

FIG. 34 shows an example transmission flow diagram for transmitting DLcommunications.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the other networks 112. By way of example, the base stations 114a, 114 b may be a base transceiver station (BTS), a Node-B, an eNode B,a Home Node B, a Home eNode B, a site controller, an access point (AP),a wireless router, and the like. While the base stations 114 a, 114 bare each depicted as a single element, it will be appreciated that thebase stations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Theother networks 112 may include wired or wireless communications networksowned and/or operated by other service providers. For example, the othernetworks 112 may include another core network connected to one or moreRANs, which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. The RAN 104 may be an access service network(ASN) that employs IEEE 802.16 radio technology to communicate with theWTRUs 102 a, 102 b, 102 c over the air interface 116. As will be furtherdiscussed below, the communication links between the differentfunctional entities of the WTRUs 102 a, 102 b, 102 c, the RAN 104, andthe core network 106 may be defined as reference points.

As shown in FIG. 1C, the RAN 104 may include base stations 140 a, 140 b,140 c, and an ASN gateway 142, though it will be appreciated that theRAN 104 may include any number of base stations and ASN gateways whileremaining consistent with an embodiment. The base stations 140 a, 140 b,140 c may each be associated with a particular cell (not shown) in theRAN 104 and may each include one or more transceivers for communicatingwith the WTRUs 102 a, 102 b, 102 c over the air interface 116. In oneembodiment, the base stations 140 a, 140 b, 140 c may implement MIMOtechnology. Thus, the base station 140 a, for example, may use multipleantennas to transmit wireless signals to, and receive wireless signalsfrom, the WTRU 102 a. The base stations 140 a, 140 b, 140 c may alsoprovide mobility management functions, such as handoff triggering,tunnel establishment, radio resource management, traffic classification,quality of service (QoS) policy enforcement, and the like. The ASNgateway 142 may serve as a traffic aggregation point and may beresponsible for paging, caching of subscriber profiles, routing to thecore network 106, and the like.

The air interface 116 between the WTRUs 102 a, 102 b, 102 c and the RAN104 may be defined as an R1 reference point that implements the IEEE802.16 specification. In addition, each of the WTRUs 102 a, 102 b, 102 cmay establish a logical interface (not shown) with the core network 106.The logical interface between the WTRUs 102 a, 102 b, 102 c and the corenetwork 106 may be defined as an R2 reference point, which may be usedfor authentication, authorization, IP host configuration management,and/or mobility management.

The communication link between each of the base stations 140 a, 140 b,140 c may be defined as an R8 reference point that includes protocolsfor facilitating WTRU handovers and the transfer of data between basestations. The communication link between the base stations 140 a, 140 b,140 c and the ASN gateway 215 may be defined as an R6 reference point.The R6 reference point may include protocols for facilitating mobilitymanagement based on mobility events associated with each of the WTRUs102 a, 102 b, 100 c.

As shown in FIG. 1C, the RAN 104 may be connected to the core network106. The communication link between the RAN 104 and the core network 106may defined as an R3 reference point that includes protocols forfacilitating data transfer and mobility management capabilities, forexample. The core network 106 may include a mobile IP home agent(MIP-HA) 144, an authentication, authorization, accounting (AAA) server146, and a gateway 148. While each of the foregoing elements aredepicted as part of the core network 106, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MIP-HA may be responsible for IP address management, and may enablethe WTRUs 102 a, 102 b, 102 c to roam between different ASNs and/ordifferent core networks. The MIP-HA 144 may provide the WTRUs 102 a, 102b, 102 c with access to packet-switched networks, such as the Internet110, to facilitate communications between the WTRUs 102 a, 102 b, 102 cand IP-enabled devices. The AAA server 146 may be responsible for userauthentication and for supporting user services. The gateway 148 mayfacilitate interworking with other networks. For example, the gateway148 may provide the WTRUs 102 a, 102 b, 102 c with access tocircuit-switched networks, such as the PSTN 108, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and traditionalland-line communications devices. In addition, the gateway 148 mayprovide the WTRUs 102 a, 102 b, 102 c with access to the other networks112, which may include other wired or wireless networks that are ownedand/or operated by other service providers.

Although not shown in FIG. 1C, it will be appreciated that the RAN 104may be connected to other ASNs and the core network 106 may be connectedto other core networks. The communication link between the RAN 104 theother ASNs may be defined as an R4 reference point, which may includeprotocols for coordinating the mobility of the WTRUs 102 a, 102 b, 102 cbetween the RAN 104 and the other ASNs. The communication link betweenthe core network 106 and the other core networks may be defined as an R5reference, which may include protocols for facilitating interworkingbetween home core networks and visited core networks.

In a WLAN system of multiple channel width, when the communicating STAmay only be capable of transmitting and receiving on a small fraction ofthe available bandwidth, the 802.11 standards may prescribe that theremaining available frequency bandwidth remains idle for the entire BSSeven though the AP and other STAs are capable of utilizing that portionof available bandwidth. Consequently, resources in such BSSs may beunder-utilized and wasted. This problem may exist in any WLAN systemwith multiple channel widths such as, for example, 802.11n, 802.11ac and802.11af, and in 802.11ah, where some STAs in a BSS only support theminimum 1 MHz operation mode.

FIG. 2A shows an example of a WLAN BSS 200 including an AP 204, and 4STAs: STA1 202 ₁, STA2 202 ₂, STA3 202 ₃, and STA4 202 ₄. FIG. 2B showsan example MAC scheme with frequency resource wastage in a WLAN systemwith multiple channel widths, for example the WLAN BSS 200 of FIG. 2A.FIG. 2B shows transmissions over time over four channels 218_(1 . . . 4) performed by the AP and STAs in FIG. 2A. Throughout all thefigures showing example MAC schemes like FIG. 2B, the entity performingthe transmission (e.g. AP, STA1, STA2, STA3 or STA4) is indicated in thesubscript of each transmission. For illustrative purposes, it is assumedthroughout the figures that each of the channels 218 _(1 . . . 4) are 1MHz wide and that channel 218 ₁ is a primary channel, although thechannels could be any bandwidth and channels 218 _(1 . . . 4) could becontiguous or non-contiguous. In addition, the AP 204 and STAs 202_(1 . . . 4) of FIG. 2A may be operational on more or less than 4channels and any of the channels could be contiguous, or non-contiguous,located within the same band or in different frequency bands. Also, theMAC schemes illustrated in the figures are examples, and each feature orelement (e.g. type message of transmission) may be used alone withoutthe other features and elements (e.g. other types of messagetransmissions) of the described MAC schemes or in various combinationswith or without other features and elements.

In the example of FIGS. 2A and 2B, it is assumed that the AP 204 may becapable of 1 MHz, 2 MHz and 4 MHz operation mode; STA1 202 ₁ and STA4202 ₄ may be capable of 1 MHz mode; STA2 202 ₂ may be capable of 1 MHz,2 MHz and 4 MHz mode; and STA3 202 ₃ may be capable of 1 MHz and 2 MHzmode. When STA2 202 ₂ and the AP 204 communicate, the packets aretransmitted over the available frequency bandwidth which includes allfour channels 218 _(1 . . . 4), for example in data transmission 206_(AP) from the AP 204 to the STA2 202 ₂ and in acknowledgement (ACK)transmission 208 _(STA2) from STA2 202 ₂ to AP 204. Data transmission210 _(STA3) to the AP 204 and ACK 212 _(AP) to STA3 202 ₃ is limited to2 MHz or channels 218 ₁₋₂. Similarly, data transmission 213 _(STA1) tothe AP 204 and ACK 216 _(AP) to STA1 202 ₁ is limited to 1 MHz orchannel 218 ₁. The unused channels are idle frequency bands 220.Therefore, in this example, when STA1 202 ₁ or STA3 202 ₃ communicateswith the AP 204, at least half, or in the case of STA1 202 ₁,three-quarters, of the available bandwidth may be idle while other STAsin the BSS may have packets to transmit. This may limit the capacity ofa BSS and may become a bottleneck, especially for technologies such as802.11af and 802.11ah that may operate on sub 1 GHz bands and may havemuch smaller bandwidths compared to 802.11n and 802.11ac.

In examples of use cases such as smart meters, an AP may need to supportup to 6000 STAs in one BSS in 802.11ah. Due to the CSMA/CA nature of theWLAN Medium Access Control (MAC) layer, a large number of users maycause significant congestion and delay and therefore very low effectivethroughput in the BSS due to packet collisions. As illustrated above, incases of Multi-User Parallel Channel Access (MU-PCA) in WLAN systemswith multiple channel widths, a portion or sometimes the majority of thebandwidth available to a BSS may be wasted due to medium access by asingle STA which only operates on a portion of the available bandwidth.Additionally, congestion, delay and effectively no throughput may becaused by the CSMA/CA nature of the 802.11 MAC Layer functions when aWLAN system must support up to 6000 STAs in a single BSS.

The enablement of parallel medium access among multiple STAs supportingdisparate operating channel widths over the available bandwidth, whichmay be contiguous or non-contiguous, and which may be located within thesame band or in separate bands (for example, any combination of the 2.4GHz industrial, scientific and medical (ISM) band, the sub-6 GHz band,the 60-GHz band, the sub-1 GHz band, the 3.5 GHz band, or the 45 GHzband, etc.), may increase frequency bandwidth utilization and efficiencyand support a large number of STAs, for example up to 6000 STAs.

In the 80+80 channel configuration, non-contiguous aggregation may bedefined in 802.11ac for a single STA access, where the data from/to thesingle STA may be split into two streams, each transmitted on one of thetwo non-contiguous 80 MHz channels individually. This may be extended toother channel combinations and enhancements that allow packets to/frommultiple STAs to be transmitted from/to the AP on multiple frequencybands simultaneously, with one STA on one or more channels, where thewidth of the channel may depend on the STAs' and AP's supportedoperating bandwidth. In this way, the number of supported STAs may beincreased and the utilization of resources may be significantlyincreased through multi-user parallel channel access (MU-PCA). Moreover,a MU-PCA session may be assigned to a single STA to enable Single UserParallel Channel Access (SU-PCA) or single user channel aggregation,over a number of contiguous or non-contiguous channels in DL or ULdirections or in Direct Link Setup (DLS) or Tunneled Direct Link Setup(TDLS) transmissions or receptions, which is a special case of MU-PCA.

MU-PCA may be achieved by utilizing transmit/receive with symmetricalbandwidth. The term ‘symmetrical bandwidth’ means that the AP and STAsutilize the same bandwidth to transmit and to receive. The APs integratethe PHY layer design enhancement, in which case the impact on thehardware of the non-AP STAs is minimal. MU-PCA may also be achieved byutilizing transmit/receive with asymmetrical bandwidth. The term“asymmetrical bandwidth” means that the AP utilizes wideband to transmitand to receive, while STAs utilize relatively narrower frequency band totransmit and to receive. PHY layer modifications may occur at both theAP and the non-AP STAs in order to support MU-PCA.

MU-PCA may use transmit/receive with symmetrical bandwidth and may useMAC Layer and PHY Layer designs and procedures. MAC Layer designs andprocedures may consist of schemes that enable standalone downlinkMU-PCA, standalone uplink MU-PCA, combined DL/UL MU-PCA and/or MU-PCAretransmissions in case of transmission errors. PHY Layer designs andprocedures may exist in the AP for supporting MU-PCA at the AP. PHYlayer designs and procedures may impact the hardware of the AP since theAP may support simultaneous multiple connections to different STAs,however a (non-AP) STA may not be impacted in the case where itcommunicates with the AP using only channels of operating bandwidth thatit already supports.

In MAC schemes, it may be assumed that there is one primary channel foreach BSS. The primary channel may be of any bandwidth and may becontiguous or non-contiguous to the other channels. The AP and/or thenon-AP STAs may monitor the primary channel appropriately (for example,according to power-save mode protocol/procedures) if they are notactively transmitting, receiving or in doze state or other power savingmode. As discussed herein, the primary channel is assumed to be channel1 unless stated otherwise.

STAs that participate in the MU-PCA may be organized into groups eitherin a pre-arranged or ad hoc fashion for both UL, DL or combined UL andDL transmissions. The STA grouping for UL versus DL may be the same ordifferent. STAs may be grouped together according to many differentcriteria such as, for example, operating channel width, similar receivedpower at the AP, RSSI, QoS priorities, propagation delay,synchronizations, or buffered packet length, among other things. Withcoordination, the grouped STAs may be able to utilize the entire or atleast the majority of the available frequency bandwidth. For example, ifthe entire available frequency band is 4 MHz, contiguous ornon-contiguous, then a potential STA group may contain four nodes thatsupport only 1 MHz operating mode, or two nodes that support only 1 MHzoperating mode and one node that supports 2 MHz operating mode.

MU-PCA may be provided for multiple STAs simultaneously over multiplechannels of disparate bandwidth, where these channels could becontiguous or non-contiguous, located within the same frequency band ordifferent frequency bands (for example, any combination of the 2.4 GHzISM band, the 3.5 GHz band, the sub-6 GHz band, the 45 GHz band, the60-GHz band or the sub-1 GHz band, etc.). Moreover, a MU-PCA session maybe assigned to a single STA to enable SU-PCA over a number of contiguousor non-contiguous channels in DL, UL or combined UL and DL directions orin Direct Link Setup (DLS) or Tunneled Direct Link Setup (TDLS)transmissions or receptions.

The standalone DL MU-PCA may be supported by MAC schemes by using theexchanges of packets such as Group Request-To-Send (G-RTS), GroupClear-To-Send (G-CTS) and MU-PCA Management (MPM). Examples of such MACschemes are illustrated in FIGS. 6-9 and discussed in detail below,where each feature or element illustrated for the purposes of examplemay be used alone without the other features and elements of thedescribed MAC schemes or in various combinations with or without otherfeatures and elements. In the following, the format of the controlframes such as G-RTS, G-CTS, MPM as well as the transmission of thecontrol frames are described. The example frames shown in FIGS. 3, 4 and5 do not show all possible fields that may be included in the frame. Forexample, the MAC header and frame body may include other fields notshown. Moreover, the fields may appear in any order and may notnecessarily be in the order shown. For example, the Type, SubType anddestination address (DA) fields may not appear in the MAC header in theorder shown.

FIG. 3 shows an example frame format for a G-RTS control frame 300. TheG-RTS frame 300 may include a MAC header 302, frame body 304 and framecheck sequence (FCS) 306. The Frame body 304 may include a MAP field308, channel assignment fields 310 _(1 . . . N), and an additionalinformation (Info) field 312. The MAC header 302 may include a Type 314,a SubType 316, and a destination address (DA) field 318, among otherfields not shown. The G-RTS frame 300 may be, for example, a modifiedversion of an RTS frame and may contain a frame body 304 containingchannel assignment information. The G-RTS frame 300 may also beimplemented as other types of frames such as action frames, actionno-ACK frames or any other type of management or control frames. TheG-RTS frame 300 may also be implemented as an IE, a field or subfield ofa management or control frame.

In the FIG. 3 example, the G-RTS frame 300 may be identified as theG-RTS frame 300 in the MAC header 302, for example, in the Type 314 andSubType 316 fields in the MAC header 302. For example, if the Type 314and SubType 316 fields comprise bits B2, B3, B4, B5, B6, and B7, thebits could be set as shown in Table 1 to identify the frame as controltype and G-RTS subtype.

TABLE 1 B3 B2 Type Description B7 B6 B5 B4 Subtype Description 0 1Control 0 1 1 0 G-RTS

The DA field 318 in the MAC Header 302 may be set to a multicast MACaddress if the group of STAs involved in the DL MU-PCA has been formedand can be identified by the multicast MAC address. The DA field mayalternatively be set to a broadcast address and the STAs involved in theDL MU-PCA may be identified in the frame body 304 or by the Group ID inthe Physical Layer Convergence Procedure (PLCP) header (not shown). IfSU-PCA is used, the G-RTS frame 300 may also be transmitted to a unicastMAC address of the targeted STA.

The frame body 304 of the G-RTS frame 300 may contain the channelassignments 310 _(1 . . . N) for the group of STAs involved in the DLMU-PCA. The MAP field 308 of the frame body 304, which may itself beimplemented as a part of any other field or subfield or InformationElement (IE), may indicate, for example: the length of the frame body304 (i.e. the channel assignment); and the number of channel assignmentfields 310 _(1 . . . N), i.e. for how many STAs N the G-RTS containschannel assignments. Other additional information fields 312 notdiscussed may be included.

If the DA field 318 is set to the broadcast address, then each of theSTA channel assignment 310 _(1 . . . N) may have explicitidentifications (IDs) for each of STAs in the DL MU-PCA group. the IDsmay be, for example, Association ID (AID), MAC addresses or other formof IDs that the AP and the STAs have established/negotiated. If the DAfield 318 is set to a multicast address for a group, then the channelassignment fields 310 _(1 . . . N) may implicitly (e.g. by the order ofthe STA in the MU-PCA group) or explicitly contain the IDs for the DLSTAs. Each STA indicated may be assigned to one or more contiguous ornon-contiguous channels. The IDs used to explicitly indicate the DLMU-PCA group STAs in channel assignment fields 310 _(1 . . . N) may be,for example, AID, MAC addresses or other form of IDs that the AP and theSTAs have negotiated. Multiple STAs in the MU-PCA group may be assignedto the same channel if the STAs are capable of multi-user multi-inputmulti-output (MU MIMO), in which case the frame body 304 (e.g. channelassignment) may also contain the number of spatial streams assigned foreach of the MU MIMO STAs assigned to the same set of channels.

FIG. 4 shows an example frame format for a G-CTS control frame 400. TheG-CTS frame 400 may include a MAC header 402, frame body 404 and framecheck sequence (FCS) 406. The Frame body 404 may include a MAP field408, channel assignment fields 410 _(1 . . . N), and an additionalinformation (Info) field 412. The MAC header 402 may include a Typefield 414, a SubType field 416, and a DA field 418, among other fieldsnot shown. The G-CTS frame 400 may be implemented as a modified versionof a CTS frame. The G-CTS frame 400 may also be implemented as othertype of frames such as action frames, action No-ACK frames or any othertypes of management and control frames.

The frame body 404 may contain channel assignment fields 410_(1 . . . N) for STAs participating in UL MU-PCA. For example, the bitsB2-B7 in the Type field 414 and SubType field 416 in the MAC Header 402may identify the G-CTS frame 400 as a control type frame and as a G-CTSsubtype as shown in Table 2.

TABLE 2 B3 B2 Type Description B7 B6 B5 B4 Subtype Description 0 1Control 0 1 0 1 G-CTS

The DA field 418 in the MAC Header 402 may be set to a multicast MACaddress representing a group of STAs if the MU-PCA group has been formedand can be identified by the multicast MAC address. Alternatively, theDA field 418 may be set to a broadcast address and the STAs involved inthe MU-PCA may be identified in the frame body 504 or by the Group ID inthe PLCP header (not shown). If SU-PCA is used, the G-CTS frame 400 maybe transmitted to a unicast MAC address of the targeted STA.

The MAP field 408, which may be implemented as a part of another fieldin the frame body 404 or in the MAC header 402 (or in the PLCP header,not shown), may indicate the presence of information available, such aschannel assignment fields 410 _(1 . . . N) for STAs, in the G-CTS frame400. When used in the context of standalone DL MU-PCA, the G-CTS framebody 404 may contain a MAP element and may not contain the channelassignment fields 410 _(1 . . . N). Multiple STAs in the MU-PCA groupmay be assigned to the same channel if the STAs are capable of MU MIMO,in which case the channel assignment in the frame body 404 may alsocontain the number of spatial streams assigned for each of the MU MIMOSTAs assigned to the same set of channels.

FIG. 5 shows an example frame format for a MU-PCA management (MPM) frame500. The MPM 500 may include a MAC header 502, frame body 504 and FCS506. The Frame body 504 may include any of the following fields: MAPfield 508, group ID 514, starting time 516, duration 518, MU-PCA options520, STA information fields 510 _(1 . . . N) corresponding to STAs 1 toN, and additional information 512. These fields are described in moredetail in the following.

MAP field 508 may indicate the types of information contained in the MPM500. For example, the MAP field 508 may indicate how many STAInformation (Info) fields 510 _(1 . . . N) the MPM 500 contains. The MAPfield 508 may itself be implemented as a field or subfield of otherfields. Group ID 514 may indicate ID of the MU-PCA Group of STAs 1 to Nwhich may have been pre-arranged or formed in an ad hoc manner. Startingtime field 516 may indicate the starting time of the next MU-PCAsession, which may be DL or UL or combined DL/UL MU-PCA transmissionincluding a DL or UL or combined DL/UL SU-PCA transmission. The startingtime may be implicitly defined if, for example, the next frames aretransmitted at a set interval, such as a Short Interframe Space (SIFS)interval, starting at the end of the MPM 500. The Duration field 518 mayindicate the duration of the next MU-PCA session. The duration may beimplicitly defined by the value included in a duration field in the MACheader 502 (not shown).

The MU-PCA Options fields 520 may indicate the options for the MU-PCAsession, such that the options include: UL MU-PCA, DL MU-PCA, combinedUL/DL MU-PCA. The MU-PCA Options fields 520 may similarly be used toindicate the equivalent SU-PCA options if the MPM 500 is transmitted toa single STA. Each STA information field 510 _(1 . . . N) may containthe information for a respective STA 1 through N regarding the upcomingMU-PCA session. Each STA Info field STA 510 _(1 . . . N) may containsubfields with information (note: the subfields are not explicitly shownin FIG. 5). For example, a STA ID subfield may indicate the ID of theSTA which may be implemented as MAC address, AID, or other IDs that theAP and STAs have agreed upon. A STA ID subfield may not be used if, forexample, the MPM is a unicast frame to a particular STA and the MPM isused to initiate a SU-PCA transmission. In another example, the STA IDsubfield may not be used if a MU-PCA group has been formed and the orderof the STAs in the MU-PCA group has been determined so that each STAbelonging to the MU-PCA may be aware which subfield contains theinformation for itself.

In another example, channel assignment subfield(s) may indicate a numberof channels assigned to the STA as well as the location of the channelsassigned. The location of the channels may be implemented usingparameters such as channel numbers, center frequencies, bandwidth,offset from the primary channel, or frequency bands, among other things.Multiple STAs in the MU-PCA group may be assigned to the same channel ifthe STAs are capable of MU MIMO, in which case the channel assignmentsubfields may also contain the number and/or order of spatial streamsassigned for each of the MU MIMO STAs assigned to the same set ofchannels.

Control packets such as G-RTS, G-CTS, ACK and MPM in the context ofstandalone DL MU-PCA may be transmitted in multiple modes. They may betransmitted on each of the individual channels (for example, asillustrated in FIGS. 6-9, as will be discussed in detail below) toprovide correct network allocation vector (NAV) settings for all STAsthat utilize the channels, in the same or overlapping BSSs. On the otherhand, the control frames may be modulated and transmitted over multiplechannels (for example, using a larger IFFT) if STAs are aware oftransmission over a larger bandwidth and capable of receiving suchtransmission. For example, G-RTS, G-CTS and ACKs may be sent across twochannels, for example channels 2 and 3, if only STAs supporting 2 MHzmode are assigned to operate on channels 2 and 3 across the entirenetwork coverage area, in which case all STAs may be receiving andsetting their NAV correctly.

In the following, all Figures illustrating MAC schemes reference theentities in the example BSS of FIG. 2A, where communication by the AP204 and STA1-STA4 202 _(1 . . . 4) is over channels 218 _(1 . . . 4),where a subscript indicates the transmitting entity. As explained above,for illustrative purposes, it is assumed that each of the channels 218_(1 . . . 4) are 1 MHz wide and that channel 218 ₁ is a primary channel.Furthermore, Short Interframe Space (SIFS) interval is used as anexample inter frame spacing, however, any other types of inter framespacing (IFS) may be used including reduced IFS (RIFS), and arbitrationIFS (AIFS).

Examples of behavior of the AP and STAs using DL MU-PCA with controlframes transmitted over the entire bandwidth, and over the primarychannel only, are shown in FIGS. 6 and 7, respectively. FIG. 6 showsexample MAC schemes 600 for enabling DL MU-PCA using control frames overthe entire available bandwidth. In the example of FIG. 6, after APtransmission 204 _(AP) of a data packet to STA2, which is capable ofsupporting transmission/reception over the entire available bandwidth,and ACK transmission 206 _(STA2) back to the AP, the AP may conductclear channel assessment (CCA) on all available bandwidth.

After obtaining access to all available channels, the AP may send outG-RTS 606 _(AP) with channel assignment on all channels 218 _(1 . . . 4)for any of the following functions: to alert the group of STAsparticipating in the DL MU-PCA of the channels that they may switch toreceive their DL packets from the AP; to reserve all channels till atleast all DL MU-PCA packets have been ACKed by the STAs by setting NAVfor all STAs operating on these channels, and potentially using them astheir own primary channel. If one of the channels 218 _(1 . . . 4) isalready occupied by some other STAs, then G-RTS 606 _(AP) may not besent on that channel and no STAs in the DL MU-PCA group may be assignedto that channel.

The STAs in the DL MU-PCA group may switch to the channels assigned tothem and switch to the correct operating mode, for example: STA1 isassigned to channel 1 218 ₁ so it may switch to channel 1 218 ₁ andoperate using 1 MHz mode; STA3 is assigned to channels 2 and 3 218 ₂₋₃so it may switch to channels 2 and 3 and operate using 2 MHz mode; STA4is assigned to channel 4 218 ₄ so it may switch to channel 4 andoperates using 1 MHz mode.

Accordingly, the STAs may respectively transmit G-CTS (or simply CTS)608 _(STA1), 608 _(STA3) and 608 _(STA4). These G-CTSs may alert the APof their readiness for receiving their DL packets, and may reserve thechannel(s) till at least all DL MU-PCA packets have been ACKed by theSTAs by setting NAV for all nodes operating on these channels,potentially using them as their own primary channel. For example, theduration field of a (G-)CTS may be set to the value ofDuration_G-RTS−SIFS_Time−(G-)CTS_Time, where Duration_G-RTS is theduration setting contained in the G-RTS packet, SIFS_Time is theduration of the SIFS 610 and (G-) CTS_Time is the transmission time ofthe G-CTS packet.

Upon receiving the (G-)CTS 608 _(STA1), 608 _(STA3) and 608 _(STA4) fromeach STA, the AP may transmit the data packets 612 _(AP) to eachrespective STA on their assigned channels. Since the data packets may beof different length and may be transmitted using different MCS, thelongest packet may be chosen to be transmitted on the primary channel218 ₁ so that the entire BSS may rely on the timing of the primarychannel to stay synchronized for BSS-wide operations. Padding 614 _(AP)may be transmitted by the AP on any channel to make the data packets ofequal length (in time) so that the DL transmissions on all channels 218_(1 . . . 4) end at the same time. Once the STAs receive theirrespective data packets, they may respectively send out ACK packets 616_(STA1), 616 _(STA3) and 616 _(STA4) to the AP to indicate successfulreception.

For STAs that are monitoring the channels, when they receive a G-RTSfrom the AP that is not addressed to them, they may cancel the NAV if notransmission from the AP has been detected after waiting for a durationof time, that may be equal to, for example(G-)CTS_Time+2×SIFS_Time+Y×A_Slot_Time+aPHY-RX-START-Delay, where(G-)CTS_Time is the duration of a (G-)CTS packet 608 _(STAX), SIFS_Timeis the duration of SIFS 610, A_Slot_Time is the duration of a slot,aPHY-RX-START-Delay may be a delay in the PHY layer pertaining to startof reception, and Y may be an configurable parameter.

The MAC DL MU-PCA scheme shown in FIG. 6 assumes that the STAsparticipating in the DL MU-PCA are capable of switching channels as wellas switching between transmission and reception modes within the SIFSinterval. If, however, the STAs are not capable of switching channelswithin the SIFS interval, the initial control packet exchanges must takeplace on the primary channel, as shown in FIG. 7.

FIG. 7 shows an example MAC scheme 700 for standalone DL MU-PCA usingG-RTS and G-CTS on the primary channel. The AP may conduct CCA on allavailable channels. After obtaining access to all channels, the AP maysend out G-RTS 702 with channel assignment on all channels. The G-RTS702 transmission may be used to reserve all channels till at least allDL MU-PCA packets have been ACKed by the STAs by setting NAV for allnodes operating on these channels, potentially using them as their ownprimary channel, and to alert the group of STAs participating in the DLMU-PCA of the order that they should send their (G-)CTS on the primarychannel with SIFS interval 710 between each STA's (G-)CTS, as well asthe channels that the STAs should switch to receive their DL packetsfrom the AP. In order to provide sufficient time for STAs to switchchannels, the STA that is assigned to receive on the primary channel maybe designated by the AP the last STA of the DL MU-PCA group to transmitits CTS (or G-CTS).

The STAs may then transmit (G-)CTS 604 _(STA4), 606 _(STA3) and 608_(STA1) sequentially on the primary channel according to the orderassigned by the AP, with a SIFS interval between each (G-)CTS. (G-)CTS604 _(STA4), 606 _(STA3) and 608 _(STA1) may serve to alert the AP oftheir readiness to switch channels to receive their DL packets, andreserve the channel(s) till at least all DL MU-PCA packets have beenACKed by the STAs by setting NAV for all nodes operating on thesechannels, potentially using them as their own primary channel. Forexample, the duration field of the nth (G-)CTS may be set toDuration_G-RTS−Y×SIFS_Time−Y×(G-) CTS_Time, where Duration_G-RTS is theduration setting contained in the G-RTS packet, SIFS_Time is theduration of the SIFS and (G-)CTS_Time is the transmission time of a(G-)CTS packet.

The first STA assigned to transmit in the MU-PCA group (in this exampleSTA4) may transmit a (G-)CTS a SIFS time after the first G-RTS frame;upon receiving the (G-)CTS 604 _(STA4) from the first STA, STA4, the APmay transmit another G-RTS (or another control frame, for example,G-Poll) on the primary channel to the next STA (in this example, STA3)to request a (G-)CTS from the second STA; the second STA may respondwith a (G-)CTS; the process may then repeat until all STAs in the MU-PCAgroup have transmitted their (G-)CTS frames. The duration field in theG-RTS and (G-)CTS frames may be adjusted accordingly with the durationsof the additional SIFSs and G-RTS frames.

The STAs in the DL MU-PCA group may switch to the channels assigned tothem and may switch to the correct operating mode. For example, STA1 isassigned to Channel 1 218 ₁ so it may stay on Channel 1 218 ₁ andoperate using 1 MHz mode; STA3 is assigned to channels 2 and 3 218 ₂₋₃so it, may switch to channels 2 and 3 and operate using 2 MHz mode; STA4is assigned to channel 4 218 ₄ so it may switch to channel 4 andoperates using 1 MHz mode.

Upon receiving the G-CTS 604 _(STA4), 606 _(STA3) and 608 _(STA1), theAP may transmit the data packets 712 _(AP) to each respective STA ontheir respectively assigned channels. Since the data packets 712 _(AP)may be of different lengths and could be transmitted using differentMCS, the longest packet may be chosen to transmitted on the primarychannel so that the entire BSS may rely on the timing of the primarychannel to stay synchronized for BSS-wide operations. Padding may beused on all channels 218 ₁₋₄ to make the data packets of equal length(in time) so that the DL transmissions end at the same time. If oneG-CTS is not received, the AP may choose to not to transmit the DLpacket for the corresponding STA on its assigned channel or it maychoose to proceed with transmission as normal. Once the STAs receivetheir respective data packets, they send out ACK packets 716 _(STA1),716 _(STA3), and 716 _(STA4) to the AP to indicate the reception.

For STAs that are monitoring the channels, when they receive a G-RTSfrom the AP that is not addressed to them, they may cancel the NAV if notransmission from the AP has been detected after waiting for a period oftime. For example, the period of time may be equal toN×G-CTS_Time+(N+1)×SIFS_Time+Y×A_Slot_Time+aPHY-RX-START-Delay, where Nis the number of STAs contained in the channel assignments in the G-RTSpacket, G-CTS_Time is the duration of a G-CTS packet, SIFS_Time is theduration of SIFS, A_Slot_Time is the duration of a slot,aPHY-RX-START-Delay may be a delay in the PHY layer pertaining to startof reception, and Y may be a configurable parameter based on the WLANsystems.

FIG. 8 shows an example MAC scheme 800 for enabling DL MU-PCA usingcontrol frames over the entire available bandwidth, and which alsoenables MU-PCA for WiFi STAs, which may be adherent to existing WiFistandards and drafts and may not be able to interpret MPM, G-RTS andG-CTS frames.

In the example of FIG. 8, an AP transmission 802 _(AP) of a data packetto STA2, which is capable of supporting transmission/reception over theentire available bandwidth 218 _(1 . . . 4), may be acknowledged bySTA2's ACK 804 _(STA2). The AP may transmit an MPM frame 806 _(AP),which may contain the options indicating that it is a DL MU-PCA (or DLSU-PCA) transmission announcement with channel assignments for each STAin the MU-PCA group. In an example, the AP may conduct CCA on allavailable bandwidth 218 _(1 . . . 4) and may transmit MPM 806 _(AP) onall channels 218 _(1 . . . 4). The MPM frames 806 _(AP) may containinformation in their MAC header to set NAV on all channels 218_(1 . . . 4) for the entire MU-PCA session. In another example, the MPMmay not contain NAV setting information; the AP may access the medium onall channels 218 _(1 . . . 4) using an IFS 810 that is sufficientlyshort (for example short IFS (SIFS) or point IFS (PIFS)) to allow the APto maintain access to the medium so that the AP may transmit RTS frames808 _(AP) (or G-RTS frames) on all channels 218 _(1 . . . 4) to initiatethe DL MU-PCA session.

In an example, the AP may conduct CCA only on the primary channel 218 ₁and transmit MPM frame 806 _(AP) on the primary channel 218 ₁. The MPMframe 806 _(AP) may announce the DL MU-PCA (or DL SU-PCA) session andsubsequently, the AP may conduct CCA on all channels 218 _(1 . . . 4)and when it has access on all channels 218 _(1 . . . 4), it may transmitan RTS frame 808 _(AP) (or G-RTS frames) on all channels 218_(1 . . . 4) to initiate the DL MU-PCA session.

After obtaining access to all available channels 218 _(1 . . . 4), theAP may send out RTS (or G-RTS) frames 808 _(AP) so that it may alert thegroup of STAs participating in the DL MU-PCA that they may switch totheir assigned channel to receive their DL packets from the AP; and sothat it may reserve all channels 218 _(1 . . . 4) until at least all DLMU-PCA packets have been ACKed by the STAs by setting NAV for all nodesoperating on these channels, potentially using them as their own primarychannel. If one of the channels is already occupied by some other STAs,then no RTS or G-RTS may be sent on that channel and no STAs in the DLMU-PCA group may be assigned to that channel.

For WiFi STAs that may not be able to interpret MPM or G-RTS frames, theAP may assign these STAs on the primary channel or any set of contiguousor non-contiguous channels including the primary channel that the legacyWiFi STAs that are capable of operating. If legacy WiFi STAs areinvolved in the MU-PCA sessions, the AP may transmit RTS on all channelsor at least may transmit RTS on the channels that the legacy WiFidevices are assigned to after having sent the MPM frames to all (other)STAs first.

In an example, if STA1 is a 802.11n STA with its primary channel beingchannel 1, it may operate on 40 MHz bandwidth on both channels 1 and 2.The AP may assign STA1 on channels 1 and 2 for a 40 MHz operation. TheAP may assign other STAs that are able to interpret MPM or G-RTS onchannels 3 and 4. The AP may then transmit RTS frames 808 _(AP) onchannels 1 and 2 or on all channels 1-4 to initiate the MU-PCA sessions.In another example, if STA1 is a 802.11ac STA with its primary channelbeing channel 1 with an 80 MHz bandwidth, and STA1 is capable of 80+80non-contiguous operation, the AP may assign STA1 on channels 1 and 3using 80+80 non-contiguous operation. The AP may then assign other STAsthat are able to interpret MPM or G-RTS on channels 2 and 3. The AP maythen transmit RTS frames on channels 1 and 3 or on all channels 1-4 toinitiate the MU-PCA sessions.

The STAs in the DL MU-PCA group may switch to the channels assigned tothem and switch to the correct operating mode. In an example, STA1 maybe assigned to channel 1 so it may switch to Channel 1 and operate using1 MHz mode; STA3 may be assigned to Channels 2 and 3 so it may switch toChannels 2 and 3 and operate using 2 MHz mode; STA4 may be assigned toChannel 4 so it may switch to Channel 4 and operate using 1 MHz mode.

Referring back to the example of FIG. 8, the STAs (STA1, STA3, STA4) maythen transmit CTS (or G-CTS) 809 _(STA1), 809 _(STA3) and 809 _(STA4) ontheir respectively assigned channel(s) so that they may: alert the AP oftheir readiness for receiving their DL packets; and reserve thechannel(s) until at least all DL MU-PCA packets have been ACKed by theSTAs by setting NAV for all nodes operating on these channels,potentially using them as their own primary channel. For example, theduration field of the G-CTS may be set toDuration_G-RTS−SIFS_Time−G-CTS_Time, where Duration_G-RTS is theduration setting contained in the RTS (or G-RTS) packet 808 _(AP),SIFS_Time is the duration of the IFS 810 and G-CTS_Time is thetransmission time of the G-CTS packet. A STA may transmit a CTS frame ifit receives a RTS from the AP, and the STA may transmit G-CTS if itreceives a G-RTS from the AP.

Upon receiving CTS (or G-CTS) 809 _(STA1), 809 _(STA3) and 809 _(STA4),the AP may transmit the data packets 812 _(AP) to each STA (STA1, STA3,STA4) on their respectively assigned channels. Since the data packets812 _(AP) could be of different length (for example, the data packet 812_(AP) on channel 1 is longer than the data packets 812 _(AP) on theother channels) and could be transmitted using different MCS, thelongest packet could be chosen to be transmitted on the primary channel218 ₁ so that the entire BSS may rely on the timing of the primarychannel 218 ₁ to stay synchronized for BSS-wide operations. Padding 814_(AP) may be used on all channels 218 _(1 . . . 4) to make the datapackets of equal length in time so that the DL transmissions on allchannels 218 _(1 . . . 4) end at the same time. Once the STAs (STA1,STA3, STA4) receive their respective data packets, they may send out ACKpackets 816 _(STA1), 816 _(STA3) and 816 _(STA4) on their respectivelyassigned channels to indicate the reception.

For STAs that are monitoring the channels, when they receive a MPM, RTSor G-RTS from the AP that is not addressed to them, they may cancel theNAV if no transmission from the AP has been detected after waiting forT_handshake+Y×A_Slot_Time+aPHY-RX-START-Delay, where T-Handshake is thetime for transmitting all packets to start the MU-PCA transmissionsincluding durations of frames such as MPM, RTS, G-RTS, CTS, G-CTS andmultiple SIFS intervals, A_Slot_Time is the duration of a slot,aPHY-RX-START-Delay may be a delay in the PHY layer pertaining to startof reception, and Y may be defined as fit for the particular WLANsystems.

In addition to the examples describe above in FIGS. 6-8, theacknowledgement of the DL MU-PCA data frames may also be implemented asBlock ACKs (BAs). FIG. 9 shows an example MAC scheme 900 for enabling DLMU-PCA using control frames and BAs. In the example of FIG. 9, the APmay transmit data 904 _(AP) (and may use padding as needed 906 _(AP)) tothe STAs (STA1, STA3, STA4) during the DL MU-PCA session 902. At the endof DL MU-PCA Session 902, the AP may immediately or with some IFS 910delay send BAR frames 908 _(AP) on all channels 218 _(1 . . . 4). TheSTAs (STA1, STA3, STA4), when receiving the BAR frames 908 _(AP) may useBAs 912 _(STA1), 912 _(STA3), and 912 _(STA4), to ACK the DL MU-PCA dataframes 904 _(AP) they received from the AP. In another example, at theend of DL MU-PCA Session, the STAs may use BAs to ACK the DL MU-PCA dataframes they received from the AP. In another example, at the end of theDL MU-PCA Session, the AP may immediately or with some IFS delay sendBAR frames on the primary channel(s). The STA that ranked as the firstSTA in the MU-PCA group may transmit a BA to the AP to acknowledge theDL MU-PCA frames it received from the AP; once the AP receives the BAfrom the first STA in the DL MU-PCA group, it may send a Block ACKRequest frame (BAR) to a second STA in the MU-PCA group; and the secondSTA may then reply with a BA. This process may continue until all STAsin the MU-PCA group have transmitted their BA to the AP to acknowledgethe DL MU-PCA frames they have received from the AP.

The standalone UL MU-PCA may be supported by MAC schemes such as theexamples illustrated in FIGS. 12-15 (described below) by exchangingpackets such as Uplink Request (ULR), Group-Poll (G-Poll), Group-ACK(G-ACK) and G-CTS. In order to provide detailed description of the threeMAC schemes, the format of the control frames such as URL, G-Poll, G-ACKas well as the transmission of the control frames are first described.The example frames shown in FIGS. 10 and 11 do not show all possiblefields that may be included in the frame. For example, the MAC headerand frame body may include other fields not shown. Moreover, the fieldsmay appear in any order and may not necessarily be in the order shown.For example, the Type, SubType and DA fields may not appear in the MACheader in the order shown.

FIG. 10 shows an example frame format of the Uplink Request frame (ULR)1000. The ULR 1000 may include a MAC header 1002, a frame body 1004, andFCS 1006. The Type field 1014 and Subtype field 1016 in the MAC Header1002 may indicate that the frame is of the type ULR (other fields 1018in the MAC Header 1002 may be included). For example, the bits of theType Field 1014 and Subtype field 1016 may be set according to Table 3.

TABLE 3 B3 B2 Type Description B7 B6 B5 B4 Subtype Description 0 1Control 0 1 0 0 ULR

The frame body 1004 of ULR 1000 may include the specifications or uplinkdetails of the data to be sent to the AP using UL MU-PCA such as, forexample, maximum allowed delay 1008, data size 1010, MCS 1012 used totransmit and other information 1020 such as QoS priority, among otherthings. In an example, the data size 1010 and MCS 1012 may be combinedinto one field that represents the duration or transmission opportunity(TXOP) duration that the STA is requesting. The URL 1000 may beimplemented as any type of frame such as action frames, action no-ACKframes or any other type of management or control frames, or as an IE,field and subfield of a management and control frame.

FIG. 11 shows an example frame format of the Group-Poll (G-Poll) frame1100. The G-Poll frame 1100 may include a MAC header 1102, a frame body1104, and FCS 1106. The Type field 1114 and Subtype field 1116 mayindicate that the G-Poll frame 1100 is of the type G-Poll. For example,the Type Field 1114 and Subtype field 1116 may be set according to Table4.

TABLE 4 B3 B2 Type Description B7 B6 B5 B4 Subtype Description 0 1Control 0 0 1 1 G-Poll

The DA field 1118 in the MAC Header 1102 may be set to a multicast MACaddress representing a group of STAs if the MU-PCA group has been formedand may be identified by the multicast MAC address. In another example,the DA field 1118 may be set to a broadcast address and the STAs beingpolled may be identified in the frame body 1104 or by the Group ID inthe PLCP header (not shown). The G-Poll frame 1100 may also betransmitted to the unicast MAC address of the targeted STA.

The MAP field 1108, which may be in the frame body or MAC header 1102 orPLCP header (not shown), may indicate how many STAs are being polled andother information that is contained in the frame body. The STA IDs 1110_(1 . . . N) of the STA could be, for example, associate IDs (AIDs), MACaddresses or other form of IDs that the AP and the STAs may haveestablished beforehand. If G-Poll is transmitted to a pre-establishedgroup of STAs, STA IDs may be omitted. The information 1112 contained inthe frame body 1104 could be for example channels assigned to the STAson which the STAs should transmit their ULR in response to the receptionof the G-Poll frame 1100. The G-Poll frame 1100 may be implemented asany type of frame such as Action Frames, Action No-ACK frames or anytype of management or control frames, or as an IE, field and subfield ofa management and control frame.

The frame format of Group-ACK (G-ACK) may be like the frame format ofthe G-Poll frame 1100 shown in FIG. 11 except Type field 1114 andSubtype field 1116 may indicate that the frame format is of the typeG-ACK, and information 1112 may be different or absent. Alternatively,assuming G-ACK has the same frame format as the G-Poll frame 1100 ofFIG. 11, the MAP field 1108 portion of the G-ACK may indicate that it isa G-ACK rather than a G-Poll. The G-ACK frame body may contain a fieldfor each STA in the group of STAs that has one or more bits toacknowledge the reception of one or more packets. Each field may alsoindicate the starting sequence number for each STA that the G-ACK frameis acknowledging. The G-ACK may be implemented as any type of framessuch as Action Frames, Action No-ACK frames or any other types ofManagement and Control frames or IEs or fields within Management andControl frames. Transmission of control packets such as G-Poll, ULR,G-CTS, and G-ACK in the context of standalone UL MU-PCA may betransmitted in multiple modes and may follow the same rules as describedpreviously for the transmission of MPM frames.

FIG. 12 shows an example MAC scheme 1200 supporting UL MU-PCA for datawithout strict delay bound. STAs, when they obtain the access to thechannel, or when they are being polled, or when transmitting packets tothe AP, may send an ULR or piggyback an ULR onto previous UL packets tothe AP to inform the AP that they have uplink packets to send and mayalso include specifications of these packets such as, for example,delay, data size, MCS used, or time/TXOP requested, among other things.In the example of FIG. 12, STA4, STA3 and STA1 transmit ULR 1202_(STA4), 1204 _(STA3), and 1206 _(STA1) sequentially on the primarychannel 218 ₁ to the AP.

AP may alert the STAs that it has received the ULR(s) with a (G-)ACKtransmission 1208 _(AP) (i.e., an ACK or G-ACK frame), either as anindividual frame or as a piggybacked part of a transmit packet. The APmay not transmit a (G-)ACK if the UL MU-PCA is scheduled to startshortly after the AP receives the ULRs. If the delay limit as specifiedin the ULR frame has passed and there was no G-ACK or other piggybackedform of the G-ACK received from the AP, the STA may assume that thetransmission of the ULR has failed and it may choose to send anotherULR, either separately or piggybacked onto another packet (for example,as a part of an aggregated MAC protocol data unit (A-MPDU) or anaggregated service protocol data unit (A-MSDU)). It may choose to sendthe data packet directly to the AP.

In the example of FIG. 12, after obtaining the available channels, theAP may transmit G-CTS 1212 _(AP) with channel assignments to the STAsparticipating in the UL MU-PCA, which may do any of the following: alertthe STAs participating in the UL MU-PCA of the channels they areassigned to transmit UL packets; align the start of all UL transmissionsfrom the STAs; and/or reserve the medium on all available channels bysetting the duration field of the G-CTS and therefore the NAV of allmonitoring STAs on these channels till the end of the ACKs by the AP toall UL data packets. The duration field of G-CTS 1212 _(AP) may be setto, for example, 2×SIFS_Time+Max_Data_Duration+ACK_Duration, whereSIFS_Time may be the duration of the SIFS 1210 interval, ACK_Durationmay be the duration of the ACK frame 1216 _(AP) and theMax_Data_Duration may be the transmission of the longest data packet intime 1214 _(STA1) transmitted on all available channels 218_(1 . . . 4), which may be calculated using the Data Size field and MCSfield included in each ULR frame 1202 _(STA4), 1204 _(STA3), and 1206_(STA1). The AP may also assign the longest UL data packet (in time) tobe transmitted on the primary channel 218 ₁.

The STAs in the UL MU-PCA group (STA1, STA3, and STA4) may transmituplink packets 1214 _(STA1), 1214 _(STA3), and 1214 _(STA4),respectively, to the AP on their assigned channel(s) (e.g. STA1 onchannel 218 ₁, STA3 on channels 218 ₂₋₃ and STA4 on channel 218 ₄).

AP may wait for an additional SIFS 12010 after the end of the longest ULdata packet in time, and may transmit ACKs 1216 _(AP) (or BAs) to alertthe reception of the UL packets. Alternatively, the AP may send aGroup-ACK, which is a jointly-encoded ACK, for all UL packets instead ofdoing it one-by-one, either over the entire bandwidth 218 _(1 . . . 4)or on the primary channel 218 ₁.

FIG. 13 shows an example MAC scheme 1300 supporting UL MU-PCA for datawith strict delay bound. This type of UL MU-PCA may be used, forexample, for high priority STAs where the AP may periodically poll theSTAs for UL packets. After obtaining the channel over all availablebandwidth 218 _(1 . . . 4), the AP may send G-Poll frames 1302 _(AP) onthe available channels 218 _(1 . . . 4), which may serve to: poll STAsfor uplink packets; alert STAs their assigned channels on which they mayreply with a ULR packet; and/or reserve the channel by setting theduration field, and therefore the NAV for STAs monitoring the channels.The STAs (STA1, STA3, and STA4) in the UL MU-PCA group may switch totheir respective assigned channels (STA1 to 218 ₁, STA3 to 218 _(2,3)and STA4 to 218 ₄) and the appropriate transmitting mode and may replyto the G-Poll frames 1302 _(AP) with ULR packet transmissions 1304_(STA1), 1304 _(STA3), and 1304 _(STA4) over their respective channelsto inform the AP of any UL packets they may have.

AP may transmit G-CTS 1306 _(AP) with channel assignments to the STAsparticipating in the UL MU-PCA, which may do any of the following: alignthe start of all UL transmissions 1308 _(STA1), 1308 _(STA3) and 1308_(STA4), from the STAs; reserve the medium on all available channels 218_(1 . . . 4) by setting the duration field of the G-CTS 1306 _(AP) andtherefore the NAV of all monitoring STAs (STA1, STA3, and STA4) on thesechannels until the end of the ACK frames 1312 _(AP) by the AP to all ULdata packets 1308 _(STA1), 1308 _(STA3) and 1308 _(STA4). The durationfield of the G-CTS 1306 _(AP) may be set to2×SIFS_Time+Max_Data_Duration+ACK_Duration, where SIFS_Time may be theduration of the SIFS interval 1310, ACK_Duration may be the duration ofthe ACK frame 1312 _(AP) and the Max_Data_Duration may be thetransmission of the longest data packet in time (1308 _(STA1) in thisexample) transmitted on all available channels 218 _(1 . . . 4), whichmay be calculated using the Data Size field and MCS field included ineach ULR frame 1304 _(STA1), 1304 _(STA3), and 1304 _(STA4). The AP mayalso assign the longest UL data packet in time (1308 _(STA1) in thisexample) to be transmitted on the primary channel 218 ₁. All STAs in theUL MU-PCA group (STA1, STA3, and STA4) may transmit uplink packets 1308_(STA1), 1308 _(STA3) and 1308 _(STA4) to the AP on their respectivelyassigned channel(s). AP may wait for an additional SIFS interval 1310after the end of the longest UL data packet in time 1308 _(STA1) and maytransmit ACKs 1312 _(AP) (or BAs) to alert the reception of the ULpackets 1308 _(STA1), 1308 _(STA3) and 1308 _(STA4).

For STAs that are monitoring the channels (for example, STA2), when theyreceive a G-Poll frame 1302 _(AP) from the AP that is not addressed tothem, they may cancel the NAV if no transmission from the AP has beendetected after waiting forULR_Time+2×SIFS_Time+Y×A_Slot_Time+aPHY-RX-START-Delay, where ULR_Timeis the duration of a ULR packet 1304 _(STA4), SIFS_Time is the durationof SIFS 1310, A_Slot_Time is the duration of a slot, aPHY-RX-START-Delaymay be a delay in the PHY layer pertaining to start of reception, and Yis a configurable parameter.

As an alternative to FIG. 13, FIG. 14 shows an example MAC scheme 1400supporting UL MU-PCA for data where the ULR packets are transmittedsequentially. Just like in FIG. 13, The AP may transmit G-Poll 1402_(AP) to the STAs in the MU-PCA group. The ULR packets 1404 _(STA4),1406 _(STA3), and 1408 _(STA1) from the STAs in the UL MU-PCA group maybe sent sequentially over the primary channel 218 ₁ for STAs that cannotswitch channels and operation mode quickly. The G-Poll 1402 _(AP) sentby the AP may have the STA assigned to transmit on the primary channel(in this example, STA1) transmitting its ULR frame as the last in theorder of ULR transmissions 1404 _(STA4), 1406 _(STA3), and 1408 _(STA1)in order to allow other STAs in the UL MU-PCA group sufficient time toswitch channels and operation mode. Like in FIG. 13, the AP may sendG-CTS 1412 _(AP) on all channels 218 _(1 . . . 4), and it may transmitACKs 1416 _(AP) to acknowledge receipt of the data transmissions 1414_(STA1), 1414 _(STA3), and 1414 _(STA4) by the STAs (STA1, STA3, andSTA4).

In another example, the first STA in the MU-PCA group may transmit a ULRa SIFS time after the first G-Poll frame; upon receiving the ULR fromthe first STA, the AP may transmit another G-Poll (or another controlframe, for example, PS-Poll) on the primary channel to the second STA torequest a ULR from the second STA; the second STA may respond with aULR; the process may repeat until all STAs in the MU-PCA group havetransmitted their ULR frames. A STA polled by the AP may not have an ULpacket to send. In this case, the AP may assign the channel to a STAthat previously has indicated to the AP that it has UL packets.

In another example, after obtaining the channel over all availablebandwidth 218 _(1 . . . 4), the AP may send G-Poll frames on theavailable channels 218 _(1 . . . 4), which may serve to: poll STAs foruplink packets; and/or alert STAs their assigned channels on which theymay reply with a UL packet. The STAs in the MU-PCA group may switch totheir assigned channel and directly start to transmit their UL packetsto the AP after an IFS interval such as SIFS.

FIG. 15 shows an example MAC scheme 1500 supporting UL MU-PCA for datawith mixed delay requirements. A STA not belonging to a UL MU-PCA group(for example, STA2) may alert the AP that it has UL packets to send bysending a ULR 1502 _(STA2) to the AP. The indication and specificationof the UL packets may also be piggybacked onto a previous packettransmitted by the STA (STA2) to the AP. The AP may indicate to STA2 thereception of the ULR 1502 _(STA2) by transmitting a (G-)ACK frame 1504_(AP). The (G-)ACK frame 1504 _(AP) may be acknowledgement for thereception of a group of STAs that indicated they have UL packets for theAP. The (G-)ACK may be piggybacked onto another DL packet or abroadcast/multicast packet. The AP may poll a group of UL MU-PCA STAs(STA1, STA3, STA4) whether they have UL packets to transmit by sendingout G-Poll frames 1506 _(AP) with assigned channel(s) for each STA onwhich they may send ULR packets 1508 _(STA1), 1508 _(STA3), and 1508_(STA4) to the AP. A STA, for example STA4, may indicate that it doesnot have a UL packet to transmit.

AP may transmit G-CTS 1512 _(AP) with channel assignments to the STAsthat are part of the UL MU-PCA group and have UL packets to send (inthis example, STA1 and STA3). It may also send a G-CTS 1512 _(AP)containing information for STA2 that has previously indicated that ithas UL packets to transmit, which may do any of the following: instructSTA2 to switch to its assigned channel 218 ₄ and operating mode; alignthe start of all UL transmissions from the STAs; reserve the medium onall available channels 218 _(1 . . . 4) by setting the duration field ofthe G-CTS 1512 _(AP) and therefore the NAV of all monitoring STAs onthese channels until the end of the ACK 1516 _(AP) by the AP to all ULdata packets 1514 _(STA1), 1514 _(STA3) and 1514 _(STA2). The durationfield of G-CTS 1512 _(AP) may be set to2×SIFS_Time+Max_Data_Duration+ACK_Duration, where SIFS_Time is theduration of the SIFS interval 1510, ACK_Duration is the duration of theACK frame 1516 _(AP) and the Max_Data_Duration is the transmission ofthe longest data packet in time (in this example, 1514 _(STA1))transmitted on all available channels 218 _(1 . . . 4), which may becalculated using the Data Size field and MCS field included in each ULRframe 1508 _(STA1), 1508 _(STA3), and 1508 _(STA4) and/or from ULR 1502_(STA2). The AP may also assign the longest UL data packet in time (514_(STA1)) to be transmitted on the primary channel 218 ₁.

All STAs in the UL MU-PCA group with data to send (STA1 and STA3) andSTA2 may transmit uplink packets 1514 _(STA1), 1514 _(STA3) and 1514_(STA2) to the AP on their respectively assigned channel(s). AP may waitfor an additional SIFS interval 1510 after the end of the longest ULdata packet in time (1514 _(STA1)) and may transmit ACK 1516 _(AP) toalert the reception of the UL data packets 1514 _(STA1), 1514 _(STA3)and 1514 _(STA2).

In addition to the acknowledgement methods described above, theacknowledgement of UL MU-PCA frames may be implemented using BA as well.The APs may acknowledge the UL MU-PCA, for example, at the end of an ULMU-PCA Session, the AP may use BAs to ACK the UL MU-PCA data frames thatit received from the STAs on the individually assigned channels. Inanother example, at the end of a UL MU-PCA Session, the STAs mayimmediately or with some IFS delay send BAR frames on their assignedchannels. The AP, when receiving the BAR from the STAs, may use BAs toACK the UL MU-PCA data frames they received from a STA on the channel(s)assigned to that STA. In another example, at the end of a UL MU-PCASession, the STA that is ranked as the first STA in the MU-PCA group mayimmediately or with some IFS delay transmit a BAR to the AP. The AP maytransmit a BA to acknowledge the UL MU-PCA frames it received from theSTA. Once the first STA receives the BA from the AP, the second STA inthe MU-PCA frame may send BAR to the AP, and the AP may then reply witha BA. This process may continue until the AP has transmitted its BA toall STAs in the UL MU-PCA group. In another example, the AP may elect totransmit BA to all STAs in the UL MU-PCA group without the explicit BARfrom the STAs. In another example, at the end of the UL MU-PCA Session,the AP may transmit ACK or BA or a Group ACK to all STAs in the ULMU-PCA group on the primary or on all channels. A frame may be definedto acknowledge one or more frames for a group of STAs.

UL and DL MU-PCA may be further combined in order to significantlyreduce overhead of signalings in group configuration/setup. The MACschemes supporting the combined UL/DL MU-PCA are shown in FIGS. 16-20.It is worth noting that though specific MAC schemes are shown in FIGS.16-20 as examples, each feature or element can be used alone without theother features and elements of the described MAC schemes or in variouscombinations with or without other features and elements.

FIG. 16 shows an example of a MAC scheme 1600 supporting the combined DLand UL MU-PCA. Prior to beginning of this scheme, the AP may transmitany of the following: DL MU-PCA packets; and/or signaling for requestingthe UL MU-PCA transmissions, which may be piggybacked onto the G-ACKterminating the DL MU-PCA packets. After obtaining access to allavailable channels 218 _(1 . . . 4), the AP may send out G-RTS 1602_(AP) with Channel Assignment on all channels 218 _(1 . . . 4), whichmay serve to do any of the following: alert the group of STAsparticipating in the DL MU-PCA (STA1, STA3, and STA4) of the channelsthat they should switch to receive their DL packets from the AP; reserveall channels 218 _(1 . . . 4) until at least all DL MU-PCA packets havebeen ACKed by the STAs by setting NAV for all nodes operating on thesechannels, potentially using them as their own primary channel. If one ofthe channels is already occupied by some other STAs, then G-RTS may notbe sent on that channel and no STAs in the DL MU-PCA group may beassigned to that channel. Alternatively, MPM may be transmitted insteadof G-RTS 1602 _(AP).

Following the G-RTS 1602 _(AP), the STAs in the DL MU-PCA group mayswitch to the channels assigned to them and switch to the correctoperating mode. The STAs (STA1, STA3, and STA4) may then transmit(G-)CTS 1604 _(STA1), 1604 _(STA3), and 1604 _(STA4), which may do anyof the following: alert the AP of their readiness for receiving their DLpackets; reserve the channel(s) until at least all DL MU-PCA packetshave been ACKed by the STAs by setting NAV for all nodes operating onthese channels, potentially using them as their own primary channel.Upon receiving the (G-)CTS 1604 _(STA1), 1604 _(STA3), and 1604 _(STA4),the AP may transmit the data packets 1606 _(AP) (possibly with padding1608 _(AP)) to each STA (STA1, STA3, and STA4) on their respectivelyassigned channel(s). Since the data packets 1606 _(AP) could be ofdifferent lengths and could be transmitted using different MCS, thelongest packet could be chosen to be transmitted on the primary channel218 ₁ so that the entire BSS may rely on the timing of the primarychannel 218 ₁ to stay synchronized for BSS-wide operations. Padding 1608_(AP) may be used on all channels 218 _(1 . . . 4) to make the datapackets 1606 _(AP) of equal length in time so that the DL transmissionsend at the same time.

Once the STAs (STA1, STA3, STA4) receive their respective data packets1606 _(AP) and decode the data successfully, they may send out ACK, BAor G-ACK packets 1612 _(STA1), 1612 _(STA3), and 1612 _(STA4) toindicate successful reception. The Acknowledgement of the DL MU-PCApackets may not be needed until the end of the MU-PCA sessions or untilthe AP explicitly request an ACK or BA using a BAR frame. If a STA(STA1, STA3, or STA4) have UL packets to transmit to the AP, it maynotify the AP by setting a More Fragment bit in the MAC Header of theACK, BA or G-ACK frame (1612 _(STA1), 1612 _(STA3), or 1612 _(STA4)) to“1”, or use some other method of indication.

The duration field of each G-ACK frame 1612 _(STA1), 1612 _(STA3), and1612 _(STA4) may be set to equal3×SIFS_Time+Data_Duration+G-CTS_Time+ACK_Duration, where: SIFS_Time maybe the duration of the SIFS interval 1610; ACK_Duration may be theduration of a (G)ACK frame 1618 _(STA1), 1618 _(STA3), or 1618 _(STA4);Data_Duration may be calculated by using the UL data packet length (forexample, length of packets 1616 _(STA1), 1616 _(STA3), or 1616 _(STA4))and the MCS used by the DL data packet 1606 _(AP) for the respectiveSTA; and the G-CTS_Time may be the same as the duration as the previousG-CTS (1604 _(STA1), 1604 _(STA3), or 1604 _(STA4)) sent by the STA tothe AP.

In an example, ACK, BA or G-ACK frame may be omitted or delayed, suchthat the AP may indicate by signaling Reverse Direction Grant (RDG) forthe STA in the DL MU-PCA data frames that the STAs may start to transmittheir UL packets or with some delay after the DL MU-PCA transmissions.This RDG indication may be implemented by setting the RDG/More PPDUindictor in the MAC header or using other methods.

With reference to FIG. 16, the AP may transmit G-CTS 1614 _(AP) to theSTAs participating in the UL MU-PCA, where UL channel assignments may beincluded that may be different than the DL channel assignment. The G-CTS1614 _(AP) may be used for any of the following: to align the start ofall UL transmissions 1616 _(STA1), 1616 _(STA3), and 1616 _(STA4) fromthe STAs; to reserve the medium on all available channels 218_(1 . . . 4) by setting the duration field of the G-CTS and thereforethe NAV of all monitoring STAs on these channels until, for example, theend of the (G-)ACK frames 1618 _(AP) by the AP to all UL data packets1616 _(STA1), 1616 _(STA3), and 1616 _(STA4). The duration field of theG-CTS 1614 _(AP) may be set to2×SIFS_Time+Max_Data_Duration+ACK_Duration, where: SIFS_Time is theduration of the SIFS interval 1610; ACK_Duration is the duration of the(G-)ACK frame 1618 _(AP); and the Max_Data_Duration is the transmissionof the longest data packet in time (in this example, 1606 _(AP) onchannel 218 ₁) transmitted on all available channels, which is obtainedfrom the duration field of the G-ACK frames 1612 _(STA1), 1612 _(STA3),or 1612 _(STA4).

In another example where the AP indicates RDG in the DL MU-PCA dataframe, the AP may choose not to transmit G-CTS. The STAs in the ULMU-PCA may initiate UL MU-PCA transmissions if they have UL frames totransmit, possibly after some IFS delay, starting at the end of the DLMU-PCA frames on their assigned channels.

With reference to FIG. 16, following the reception of (G-)CTS 1614 _(AP)from the AP, STAs in the UL MU-PCA group (STA1, STA3 and STA4), maytransmit uplink packets 1616 _(STA1), 1616 _(STA3), and 1616 _(STA4) tothe AP on their respectively assigned channel(s) (channel 218 ₁ forSTA1, channels 218 _(2,3) for STA3 and channel 218 ₄ for STA4). AP maywait for an additional SIFS interval 1610 after the end of the longestUL data packet in time (in this example, 1616 _(STA1)) and may transmit(G-)ACK frames 1618 _(AP) to notify the STAs (STA1, STA3 and STA4) ofthe reception of the UL packets 1616 _(STA1), 1616 _(STA3), and 1616_(STA4). In another example, a jointly-encoded ACK may be transmittedacross all channels 218 _(1 . . . 4) or just on the primary channel(s)218 ₁. The ACK may also be implemented as BA or multi-user ACKs on allchannels 218 _(1 . . . 4) or just on the primary channel(s) 218 ₁, orthe AP may transmit the BAs if the STAs request them using a BAR.

FIG. 17 shows an example flow diagram 1700 of a method for combined DLand UL MU-PCA performed by a STA in a BSS system, where the STA is partof a MU-PCA group. In 1705, the STA may receive, from an AP, over achannel associated with the STA, a RTS that indicates that the AP isready to transmit data messages simultaneously to STAs in the MU-PCAgroup over available channels. In 1710, the STA may transmit to the APover the channel associated with the STA, a clear-to-send (CTS) thatindicates that the STA is ready to receive on the channel associatedwith the STA. The CTS may reserve the channel associated with the STAfor the STA for the MU-PCA session. In 1715, the STA may receive fromthe AP a data message over the channel associated with the STA, wherethe data message is part of a group of multiple simultaneous datamessages over the available channels.

In 1720, the STA may transmit to the AP a acknowledgement (ACK) message(or G-ACK or BA) over the channel associated with the STA, where the ACK(or G-ACK or BA) may include a More Fragment bit that is set to ‘1’ ifthe STA has uplink data to transmit to the AP. If the More Fragment bitis set to 1 indicating the presence of UL data at the STA, 1725, then,in 1730, the STA may receive from the AP a clear-to-send (CTS) messageover the channel assigned to the STA indicating the channel associatedwith the STA is reserved for the STA for UL transmission and the STA maytransmit its UL data to the AP over the channel associated with the STA.Any of the messages in FIG. 17 including RTS, CTS, and ACK may be groupmessages, for example, group RTS (G-RTS), group CTS (G-CTS), and groupACK (G-ACK).

FIG. 18 shows an example MAC scheme 1800 supporting the combined UL andDL MU-PCA. Prior to this MAC scheme 1800, the group of STAs may transmitany of the following: UL MU-PCA packets to the AP; and signaling for theDL MU-PCA transmissions may be piggybacked onto the G-ACK terminatingthe UL MU-PCA packets. After obtaining the channel over all availablebandwidth 218 _(1 . . . 4), the AP may send G-Poll frames 1802 _(AP) onthe available channels 218 _(1 . . . 4), which may accomplish any of thefollowing: poll STAs for uplink packets; alert STAs their assignedchannels on which they can reply with a ULR packets; and/or reserve thechannel by setting the duration field, and therefore the NAV for STAsmonitoring the channels. The STAs in the UL MU-PCA group (STA1, STA3,and STA4) may switch to the assigned channels and the appropriatetransmitting mode and may reply the G-Poll with ULR packets 1804_(STA1), 1804 _(STA3), and 1804 _(STA4) over their respectively assignedchannels (STA1 and 218 ₁, STA3 on 218 _(2,3) and STA4 on 218 ₄) toinform the AP of any UL packets they have.

AP may transmit G-CTS 1806 _(AP) on each channel 218 _(1 . . . 4) withchannel assignments to the STAs participating in the UL MU-PCA, andwhich may achieve any of the following: align the start of all ULtransmissions from the STAs 1808 _(STA1), 1808 _(STA3), and 1808_(STA4); and reserve the medium on all available channels 218_(1 . . . 4) by setting the duration field of the G-CTS 1806 _(AP) andtherefore the NAV of all monitoring STAs on these channels till the endof the (G-)ACK frames 1812 _(AP) by the AP to acknowledge all UL datapackets 1808 _(STA1), 1808 _(STA3), and 1808 _(STA4). The duration fieldof the G-CTS 1806 _(AP) may be set to2×SIFS_Time+Max_Data_Duration+ACK_Duration, where SIFS_Time may be theduration of the SIFS interval 1810, ACK_Duration may be the duration ofthe (G-)ACK frame 1812 _(AP) and the Max_Data_Duration may be thetransmission of the longest data packet in time transmitted on allavailable channels 218 _(1 . . . 4) (for example, 1808 _(STA1)), andwhich may be calculated using the Data Size field and MCS field includedin each ULR frame 1804 _(STA1), 1804 _(STA3), and 1804 _(STA4). The APmay also assign the longest UL data packet in time (for example, 1808_(STA1)) to be transmitted on the primary channel 218 ₁.

All STAs in the UL MU-PCA group (STA1, STA3, and STA4) may transmituplink packets 1808 _(STA1), 1808 _(STA3), and 1808 _(STA4) to the AP ontheir respectively assigned channel(s) (STA1 on 218 ₁, STA3 on 218_(2,3) and STA4 on 218 ₄). AP may wait for an additional SIFS interval1810 after the end of the longest UL data packet in time and if it candecode the received data packet successfully, the AP may transmit G-ACKframes 1812 _(AP) to indicate the reception of the UL packets 1808_(STA1), 1808 _(STA3), and 1808 _(STA4). If one or more UL data packetswere not correctly decoded, then the AP may not send G-ACK packets onthose corresponding channels. In an example, the AP may transmit a G-CTSaddressed to itself if the AP has DL packets to transmit to the STAsfrom which the AP did not correctly receive the UL packets. The durationfield setting of the (G-)CTS 1896 _(AP) may be the same as the durationfield setting of the G-ACKs explained below. The (G-ACKs 1812 _(AP) maybe implemented as any type of frame, for example, as ACK, BA ormulti-user ACKs frames. In an example, the acknowledgement of the ULMU-PCA packets may be omitted until the end of the MU-PCA sessions oruntil the STAs explicitly request an ACK or BA using a BAR frame.

With reference to FIG. 18, if the AP has DL packets to transmit to theSTAs, it may set the More Fragment bit in the MAC Header of the G-ACKframe 1812 _(AP) to “1” or provide an indication using any other method.The duration field of the G-ACK frame 1812 _(AP) may be set to equal to2×SIFS_Time+Data_Duration+ACK_Duration, where SIFS_Time is the durationof the SIFS interval 1810, ACK_Duration is the duration of the (G-)ACKframes 1812 _(AP), Data_Duration is calculated by using the longest DLdata packet length in time (for example, data packet 1814 _(AP) onchannel 2180. In an example where the AP does not provide ACKs, the STAsmay include a RDG indicator in the UL MU-PCA frames to provide reversedirection grand for the AP to transmit DL MU-PCA frames.

The AP may transmit its data packets 1814 _(AP) to each STA on theirassigned channels, which may be after SIFS interval 1810. Since the datapackets 1814 _(AP) could be of different length and may be transmittedusing different MCS, the longest data packet 1814 _(AP) may be chosen tobe transmitted on the primary channel 218 ₁ so that the entire BSS mayrely on the timing of the primary channel 218 ₁ to stay synchronized forBSS-wide operations. Padding 1816 _(AP) may be used on any channel 218_(1 . . . 4) to make the data packets of equal length in time so thatthe DL transmissions end at the same time. Once the STAs receive theirrespective data packets 1814 _(AP), they may send ACK packets 1818_(STA1), 1818 _(STA3) and 1818 _(STA4) on their respective channels toindicate the reception. The ACKs 1818 _(STA1), 1818 _(STA3) and 1818_(STA4) may be implemented as BA. In another example, theacknowledgement of the DL MU-PCA packets may be omitted until the end ofthe MU-PCA sessions or until the AP explicitly request an ACK or BAusing a BAR frame.

FIG. 19 shows an example MAC scheme 1900 where the UL MU-PCAtransmission are initiated by ULR transmitted sequentially on theprimary channel, where the individual messages function as describedabove with respect to other example MAC schemes. Each STA in the MU-PCA(STA1, STA3, and STA4), may transmit a ULR frame 1902STA4, 1904STA3, and1906STA1 sequentially to the AP on the primary channel 218 ₁, which theAP may acknowledge by sending a G-ACK 1908 _(AP) on the primary channel.The AP may transmit G-CTS 1912 _(AP) on each channel 218 _(1 . . . 4)with channel assignments to the STAs participating in the UL MU-PCA. TheSTAs may transmit their data 1914 _(STA1), 1914 _(STA3) and 1914 _(STA4)over their respectively assigned channels (STA1 on 218 ₁, STA3 on 218_(2,3), and STA4 on 218 ₄), and the AP may acknowledged any successfullyreceived data by transmitting a G-ACK 1916 _(AP) on the respectivechannels.

The AP may transmit its data packets 1818 _(AP) to each STA on theirassigned channels, which may be after SIFS interval 1810. Since the datapackets 1918 _(AP) may be of different length and may be transmittedusing different MCS, the longest data packet 1918 _(AP) may be chosen tobe transmitted on the primary channel 218 ₁ so that the entire BSS mayrely on the timing of the primary channel 218 ₁ to stay synchronized forBSS-wide operations. Padding 1920 _(AP) may be used on any channel 218_(1 . . . 4) to make the data packets of equal length in time so thatthe DL transmissions end at the same time. Once the STAs receive theirrespective data packets 1918 _(AP), they may send ACK packets 1922_(STA1), 1922 _(STA3) and 1922 _(STA4) on their respective channels toindicate the reception.

FIG. 20 shows an example MAC scheme 2000 enabling combined DL/UL MU-PCAusing control frames over the entire available bandwidth, which alsoenable MU-PCA for legacy WiFi STAs, which may be adherent to WiFistandards and drafts, and which may not able to interpret MPM, or G-RTS,G-CTS or G-ACK frames. The AP may initiate the MU-PCA sessions bytransmitting a MU-PCA Management (MPM) frames 2002 _(AP), which maycontain the options indicating that it is a combined DL/UL MU-PCAtransmission announcement with channel assignments for each of the STAsin the MU-PCA group (STA1, STA3, and STA4).

In an example, the AP may conduct CCA on all available channels 218_(1 . . . 4) and transmit MPM frame 2002 _(AP) on all channels 218_(1 . . . 4). The MPM frames 2002 _(AP) may contain information in theirMAC headers to set NAV on all channels for the entire MU-PCA session. Inan example, the MPM may not contain NAV setting information; instead,the AP may access the medium on all channels 218 _(1 . . . 4) using IFS2010 that is sufficiently short such as SIFS or PIFS to allow the AP tomaintain the access to the medium so that the AP may transmit (G-)RTSframes 2004 _(AP) frames on all channels 218 _(1 . . . 4) to initiatethe DL/UL MU-PCA session. In another example, the AP may conduct CCAonly on the primary channel 218 ₁ and may transmit MPM frames 2002 _(AP)on the primary channel 218 ₁. The MPM frames 2002 _(AP) may announce theDL/UL MU-PCA session and subsequently, the AP may conduct CCA on allchannels 218 _(1 . . . 4) and, upon accessing all channels 218_(1 . . . 4), it may transmit (G-)RTS frames 2004 _(AP) on all channels218 _(1 . . . 4) to continue the DL/UL MU-PCA session.

With reference to FIG. 20, after obtaining access to all availablechannels 218 _(1 . . . 4), the AP may send out RTS (or G-RTS) frames2004 _(AP) on all channels, which may serve to accomplish any of thefollowing: alert the group of STAs participating in the DL MU-PCA (STA1,STA3, STA4) that they may switch to their assigned channel to receivetheir DL packets from the AP; reserve all channels 218 _(1 . . . 4)until all DL/UL MU-PCA packets have been ACKed by the STAs by settingNAV for all nodes operating on these channels, potentially using them astheir own primary channel. If one of the channels is already occupied bysome other STAs, then a (G-)RTS may not be sent on that channel and noSTAs in the MU-PCA group may be assigned to that channel.

For legacy WiFi STAs which may not be able to interpret MPM or G-RTSframes, the AP may assign these STAs on the primary channel 218 ₁ or anycontiguous or non-contiguous channels including the primary channel onwhich the legacy WiFi STAs that are capable of operating. If legacy WiFiSTAs are involved in the MU-PCA sessions, the AP may transmit RTS frame2004 _(AP) on all channels 218 _(1 . . . 4) or at least may transmit RTSframe 2004 _(AP) on the channels that the legacy WiFi devices areassigned to after having sent the MPM frames 2002 _(AP) to all STAsfirst. In an example, if STA1 is a 802.11n STA with its primary channelbeing Channel 1, it may operate on 40 MHz bandwidth on both Channel 1and Channel 2; the AP consequently may assign STA1 on Channel 1 andChannel 2 for a 40 MHz operation. The AP may assign other STAs that areable to interpret MPM or G-RTS on Channels 3 and 4. The AP may transmitRTS frames on Channel 1 and Channel 2 or on all channels to initiate theMU-PCA sessions. In another example, if STA1 is a 802.11ac STA with itsprimary channel being Channel 1 (80 MHz), and STA1 is capable of 80+80non-contiguous operation, the AP may assign STA1 on Channel 1 andChannel 3 using 80+80 non-contiguous operation. The AP may then assignother STAs that are able to interpret MPM or G-RTS on Channel 2 andChannel 4. The AP may then transmit RTS frames on Channel 1 and Channel3 or on all channels to initiate the MU-PCA sessions.

With reference to FIG. 20, the STAs in the MU-PCA group (STA1, STA3, andSTA4) may switch to the channels assigned to them and switch to thecorrect operating mode, for example: STA1 is assigned to channel 218 ₁so it may switch to channel 218 ₁ and it may operate using 1 MHz mode;STA3 is assigned to channels 218 _(2,3) so it may switch to channels 218_(2,3) and operate using 2 MHz mode; and STA4 is assigned to channel 218₄ so it may switch to channel 218 ₄ and operate using 1 MHz mode.

The STAs may then transmit (G-)CTS 2006 _(STA1), 2006 _(STA3), 2006_(STA4), which may accomplish any of the following: alert the AP oftheir readiness for receiving their DL packets 2008 _(AP); reserve thechannel(s) until at least all DL/UL MU-PCA packets have been ACKed bythe STAs (2014 _(STA1), 2014 _(STA3), and 2014 _(STA4)) by setting NAVfor all nodes operating on these channels, potentially using them astheir own primary channel. For example, the duration field of the(G-)CTS 2006 _(STA1), 2006 _(STA3), 2006 _(STA4) may be set to Duration(G-)RTS−SIFS_Time−(G-) CTS_Time, where Duration (G-)RTS may be theduration setting contained in the (G-)RTS frame 2004 _(AP), SIFS_Timemay be the duration of the SIFS interval 2010 and (G-)CTS_Time is thetransmission time of the (G-)CTS packet 2006 _(STA1), 2006 _(STA3), 2006_(STA4). In an example, each STA in the MU-PCA group may transmit CTSframe 2006 _(STA1), 2006 _(STA3), 2006 _(STA4) if it receives an RTSframe 2004 _(AP) from the AP, or may transmit a G-CTS frame 2006_(STA1), 2006 _(STA3), 2006 _(STA4) if it receives a G-RTS frame 2004_(AP) from the AP.

Upon receiving the CTS or G-CTS 2006 _(STA1), 2006 _(STA3), 2006_(STA4), the AP may transmit the data packets 2008 _(AP) to each STA ontheir assigned channel(s). Since the data packets 2008 _(AP) may be ofdifferent length and may be transmitted using different MCS, the longestpacket may be chosen to transmitted on the primary channel 218 ₁ so thatthe entire BSS may rely on the timing of the primary channel 218 ₁ tostay synchronized for BSS-wide operations. Padding 2012 _(AP) may beused on any channel as needed to make the data packets of equal lengthin time so that the DL transmissions on all channels end at the sametime. Once the STAs receive their respective data packets 2008 _(AP) anddecode the data successfully, they may send out ACK (or BA or G-ACK)packets 2014 _(STA1), 2014 _(STA3), and 2014 _(STA4) on theirrespectively assigned channels to indicate the successful reception. Inan example, the acknowledgement of the DL MU-PCA packets 2008 _(AP) maybe omitted or delayed until the end of the MU-PCA sessions or until theAP requests an ACK or BA using a BAR frame.

If a STA has UL packets to transmit to the AP, it may set the MoreFragment bit in the MAC Header of the ACK (BA or G-ACK) frame 2014_(STA1), 2014 _(STA3), and 2014 _(STA4) to “1” or use any other methodof indication. The duration field of the (G-)ACK 2014 _(STA1), 2014_(STA3), and 2014 _(STA4) may be set equal to3×SIFS_Time+Data_Duration+(G-)CTS_Time+(G-)ACK_Duration, where SIFS_Timeis the duration of the SIFS interval 2010, ACK_Duration is the durationof an ACK frame 2014 _(STA1), 2014 _(STA3), 2014 _(STA4), Data_Durationis calculated by using the UL data packet (2018 _(STA1), 2018 _(STA3),or 2018 _(STA4)) length and the MCS used by the DL data packet 2008_(AP), and the (G-)CTS_Time may be the same as the duration as theprevious (G-)CTS 2006 _(STA1), 2006 _(STA3), or 2006 _(STA4), sent bythe STA to the AP.

In an example where the ACK (or BA or G-ACK) frame is omitted ordelayed, the AP may indicate by signaling Reverse Direction Grant (RDG)for the STA in the DL MU-PCA data frames that the STAs may starttransmitting their UL packets, possibly with some delay, after the DLMU-PCA transmissions. Such RDG indication may be implemented, forexample, by setting the RDG/More PPDU indictor in the MAC header or byany other indication method.

AP may transmit CTS or G-CTS frames 2016 _(AP) (where G_CTS may includechannel assignments, which may be different than the DL channelassignment) to the STAs participating in the UL MU-PCA over theirrespectively assigned channels. The CTS frames 2016 _(AP) may serve toaccomplish any of the following: align the start of all UL transmissions2018 _(STA1), 2018 _(STA3), and 2018 _(STA4) from the STAs; and reservethe medium on all available channels 218 _(1 . . . 4) by setting theduration field of the (G-)CTS frame 2016 _(AP) and therefore the NAV ofall monitoring STAs on these channels till the end of the ACK frames2020 _(AP) by the AP to all UL data packets 2018 _(STA1), 2018 _(STA3),and 2018 _(STA4). The duration field of the (G-)CTS frame 2016 _(AP) maybe set to 2×SIFS_Time+Max_Data_Duration+(G-) ACK_Duration, whereSIFS_Time is the duration of the SIFS interval 2010, (G-) ACK_Durationis the duration of the ACK frame 2020 _(AP) and the Max_Data_Duration isthe transmission of the longest data packet in time 2018 _(STA1)transmitted on all available channels, which is obtained from theduration field of the (G-)ACK frames 2014 _(STA1), 2014 _(STA3), and2014 _(STA4). In an example where the AP may indicate RDG in the DLMU-PCA data frame, the AP may choose not to transmit CTS or G-CTS. TheSTAs in the UL MU-PCA STAs may initiate UL MU-PCA transmissions if theyhave UL frames to transmit immediately or after some IFS delay startingat the end of the DL MU-PCA frames on their assigned channels. All STAsin the UL MU-PCA group transmit uplink packets to the AP on theirassigned channel(s).

With reference to FIG. 20, the AP may wait for an additional SIFSinterval 2010 after the end of the longest UL data packet in time 2018_(STA1) and it may transmit ACK frames 2020 _(AP) to alert the receptionof the UL packets 2018 _(STA1), 2018 _(STA3), and 2018 _(STA4). In anexample, a jointly-encoded ACK is transmitted across all channels 218_(1 . . . 4) or just on the primary channel(s) 218 ₁. The ACK frames2020 _(AP) may also be implemented as BA or multi-user ACKs all channels218 _(1 . . . 4) or just on the primary channel(s) 218 ₁, or the AP maytransmit the BAs if the STAs request them using a BAR.

In an example, the UL MU-PCA portion of the combined DL/UL or combinedUL/DL MU-PCA transmission may also be of mixed delay requirements asdescribed above similarly for the standalone UL MU-PCA transmission ifone or more STAs in the UL MU-PCA group do not have any UL packets totransmit. Similar to what was described for Standalone DL and StandaloneUL MU-PCA sessions above, the acknowledgement may be implemented by ACK,BA or multi-user ACKs. The AP and the STAs may individually requestacknowledgement by sending BARs and may receive BA as a response. The APmay also transmit multi-user ACKs to a group of STAs to acknowledge ULMU-PCA data frames.

In case one or more data packet transmission fails in the DL standalone,UL standalone or combined UL/DL MU-PCA schemes, the data packets thatfailed may need to be retransmitted. Different possible retransmissionmethods may be used. In one example, the DL or UL packets may bemaintained at the top of the transmit buffer and may be retransmitted atthe very next transmit opportunity either in a one-to-one unicasttransmission or in subsequent DL, UL or combined DL/UL MU-PCAtransmissions. Depending on the length of the packet, the long or shortretransmission timer may be increased each time a packet isretransmitted. The packet may be discarded if the retransmission timerreaches the threshold value. In another example, the medium may bereserved sufficiently long by setting the duration field of the G-RTS,G-CTS, G-Poll and or G-ACK so that there is sufficient time forretransmission of the DL or UL MU-PCA packets on the allocatedbandwidth. The NAV setting may be cancelled by the reception of the ACKpackets transmitted to signal the reception of the DL, UL MU-PCApackets.

The STAs and APs in a BSS may indicate their capabilities andpreferences for MU-PCA prior to MU-PCA transmissions and receptions. Forexample, the AP may include in its beacon, Probe Response or any othertype of frame, an indicator that the AP is capable of MU-PCA. Suchindicator may also be implemented as several indicators for capabilitiessuch as, for example, one indicator may be used for capability for ULMU-PCA and/or another indicator may be used for capability for DLMU-PCA. In another example, there may be four indicators: DL MU-PCACapable, UL MU-PCA Capable, DL SU-PCA Capable, or UL MU-PCA Capable. TheMU-PCA capability indicator(s) may be included in any existing or newfield such as an IE in any management or control frame or any other typeof frame or in MAC or PLCP headers.

Similarly, the STA may indicate its capability for MU-PCA as well usingone or more indicators for UL and DL MU-PCA, or UL and or SU-PCA, in,for example, Probe Request, Association Request, or other management orcontrol frames or any type of frames or in MAC or PLCP headers. The APand the STAs may indicate their MU-PCA preference. The MU-PCA capabilityindicator(s) may be included in any existing or new field such as in anIE in a management, control or other type of frame.

The AP MU-PCA preference (DL and/or UL) may include any of the followingitems. The AP MU-PCA preference may include MU-PCA channels relatedinformation including, for example, a number of channels available forMU-PCA or a location of MU-PCA channels. The location information may belocation of primary channel, for example, identified by any of thefollowing parameters: frequency band, channel numbers, center frequency,and/or bandwidth, among other parameters. The location information maybe location of MU-PCA non-primary channels, for example, identified byany of the following parameters: frequency band, channel numbers, offsetcompared to the primary channel or a reference channel or frequency,center frequencies, and/or bandwidth, among other parameters.

The AP MU-PCA preference may also include MU-PCA options. For example,in a MU-PCA transmission, a STA may be assigned to transmit or receiveon one or more channels, or even the entire bandwidth. In this case,examples of SU-PCA options may include any of the following: PHY layeraggregation only, MAC layer aggregation only, mixed PHY/MAC layeraggregation, contiguous aggregation only, and/or non-contiguousaggregation capable. For the option of PHY Layer aggregation only, theAP may only transmit/receive one MAC frame (including, for example,A-MPDU, or A-MSDU) to/from a STA within a MU-PCA transmission modulatedon one or more contiguous or non-contiguous channels. For the option ofMAC Layer aggregation only, the AP may transmit/receive multiple MACframes (including, for example, A-MPDUs, or A-MSDUs) to/from a STAwithin a MU-PCA transmission with each MAC frame modulated on onechannel. For the option of Mixed PHY/MAC Layer aggregation, the AP mayonly transmit/receive one or more MAC frames (including, for example,A-MPDUs, or A-MSDUs) to/from a STA within a MU-PCA transmission witheach MAC frame modulated on one or more contiguous or non-contiguouschannels. For the option of contiguous aggregation only, the AP mayallow only aggregations of contiguous channels in MU-PCA transmissions.For the option of non-contiguous aggregation capable, the AP may allowaggregation of non-contiguous channels as well as contiguous channels.

The AP MU-PCA preference may also include the maximum size of MU-PCAgroup, which may indicate the maximum number of STAs that can belong toa MU-PCA group, or in other words, the maximum number of STAs that canparticipate in MU-PCA at a given time.

The STA MU-PCA preference (DL and/or UL) may include any of thefollowing items. The STA MU-PCA preference (DL and/or UL) may includeMU-PCA channels related information and MU-PCA options. MU-PCA channelsrelated information may include, for example, any of the followinginformation: a maximal number of channels available for MU-PCA;bandwidth for each MU-PCA channels; whether bandwidth for MU-PCAchannels is dynamic or static; and/or preferred DL/UL MU-PCA channel(s).For the preferred DL/UL MU-PCA channel(s) information, the preference ofthe DL/UL MU-PCA channels may be based on, for example, the hardwareimplementation, capability, detected interference and/or noise levels,etc. Accordingly, the location of preferred DL/UL MU-PCA channels may beidentified in the information, for example, using any of the followingparameters: frequency band, channel numbers, offset compared to theprimary channel or a reference channel, frequency, center frequencies,and/or bandwidth, among other parameters.

MU-PCA options may include, for example, any of the following options:SU-PCA capable and SU-PCA options. SU-PCA capable may indicate whetherthe STA is capable of conducting SU-PCA. For SU-PCA options, in a MU-PCAtransmission, a STA may be assigned to transmit or receive on one ormore channels, or even the entire bandwidth. The SU-PCA options mayinclude, for example, any of the following options: PHY Layeraggregation only; MAC layer aggregation only; Mixed PHY/MAC layeraggregation; contiguous aggregation only; non-contiguous aggregationcapable.

For the PHY Layer aggregation only option, the STA may onlytransmit/receive one MAC frame (including A-MPDU, or A-MSDU) to/fromanother STA within a MU-PCA transmission modulated on one or morecontiguous or non-contiguous channels. For the MAC Layer aggregationonly option, the STA may transmit/receive multiple MAC frames(including, for example, A-MPDUs, or A-MSDUs) to/from another STA withina MU-PCA transmission with each MAC frame modulated on one channel. Forthe mixed PHY/MAC Layer aggregation option, the STA may onlytransmit/receive one or more MAC frames (including, for example,A-MPDUs, or A-MSDUs) to/from another STA within a MU-PCA transmissionwith each MAC frame modulated on one or more contiguous ornon-contiguous channels. For the contiguous aggregation only option, theSTA may only be capable of aggregations of contiguous channels in MU-PCAtransmissions. For the non-contiguous aggregation capable option, theSTA may be capable of aggregation of non-contiguous channels as well ascontiguous channels. In addition, the AP or the STAs may indicate changeof MU-PCA capability and/or preferences at any time using new orexisting management, control or other types of frames.

A WLAN PHY layer transceiver may support single user transmission overthe whole frequency band, or MU-MIMO transmission while each useroccupies the whole frequency band, and may use space division multipleaccess (SDMA) to distinguish users. The PHY layer transceiver schemesdiscussed below support multiple users while each user partiallyoccupies the frequency band. In the following, the transmitter andreceiver are assumed to have symmetrical bandwidth. Based on the natureof frequency location of the aggregated channels, the following areexamples of a few types of channel aggregation: contiguous channelaggregation, where aggregated channels may be contiguous in frequencydomain; non-contiguous channel aggregation, where aggregated channelsmay not be non-contiguous in frequency domain; and hybrid channelaggregation, where some of the aggregated channels may be contiguous,and others may be non-contiguous. In the following, PHY layer methodsare described, which may be utilized in any of the examples of channelaggregation. The PHY layer methods may be used in conjunction with anyof the MAC solutions presented described above. In order to avoidpotential contentions, G-CTSs may be sent by STAs on their respectivechannels to reserve transmission channels. Other STAs that want tooperate on the same channel may listen to all packets to determine ifthe channel is available. On receiving G-RTS and G-CTS, STAs may settheir NAV and have virtual carrier sense (VCS), described in detailbelow.

The IFFT and/or fast Fourier transform (FFT) size for each user may bedetermined by the smallest bandwidth defined, or configured, for use.For example, if 1 MHz is the smallest operational bandwidth of a system,then the IFFT/FFT size may be fixed to 32 corresponding to a bandwidthof 1 MHz. For other systems, the same rule may be applied. In anotherexample, the IFFT/FFT size may be different depending on the sub-carriersize, or other system design considerations such as the guard periodsize. An AP and/or STA may also choose to operate on wider bandwidth ifseveral contiguous channels are assigned to one user. When widerbandwidth is utilized, the system may have higher spectral efficiencythan a system where several channels are used separately. In thisscenario, the STA may be capable of aggregating with contiguous channelsand transmit with larger bandwidth. The STA may support differentcapabilities. The modification of STA behavior based on the associatedcapabilities of the STA is described in detail below. The following areexamples of STA behavior that may be dependent on STA capabilities.

In one example, a STA may be capable of channel aggregation. If the STAhas capability for channel aggregation and needs more data from the AP,it may pre-negotiate with the AP. Then the AP may send G-RTS requestingthe STA to send G-CTS on multiple channels. If the aggregated channelsassigned to the STA are non-contiguous, a segment parser may be utilizedto split the data from the MAC layer into different frequency channels.Transmitting and receiving on each channel may be performed by the STAusing procedures that are separately defined for each frequency channel.Depending on the different channel quality, receive signal-to-noiseration (SNR), and/or transmitter/receiver capability, both equal MCSand/or unequal MCS may be applied for aggregated channels. For equalMCS, an AP or STA may perform encoding and modulation on the data passedfrom the MAC layer, and then split them by segment parser to differentaggregated channels. In another example, the AP or STA may conductsegment parsing before encoding and modulation. For unequal MCS, eachaggregated channel may have its own MCS.

Based on different MCS levels, and AP or STA may split the bits from theMAC layer into different channels using a segment parser, and mayperform separate encoding and modulation schemes. For example if channel1 is able to handle 16 quadrature amplitude modulation (QAM) at ½ coderate and channel 2 is able to handle quadrature phase shift keying(QPSK) at rate ½ to guarantee, for example, a 10% Frame Error Rate (FER)at the receiver, then the segment parser may split twice as many bitsfor channel 1 than for channel 2. In another example, the same data maybe sent on both frequency bands (i.e. channels) to better exploitfrequency diversity.

FIG. 21 shows an example transmission flow diagram 2100 with a STAcapable of channel aggregation. In FIG. 21, it is assumed that equal MCSor unequal MCS may be applied. In this example, three MU-PCA STAs 2102_(1,2,3) are supported simultaneously at the AP side, where it isassumed that STA2 2102 ₂ occupies two channels, channels 2 and 3, thatare non-contiguously aggregated, and is capable of channel aggregation.Each MU-PCA STA 2102 _(1,2,3) may receive data x₁, x₂, and x₃(respectively) as input and may apply padding 2104 _(1,2,3) as needed tothe data. Each cSTA 2102 _(1,2,3) may apply scrambling 2106 _(1,2,3),forward error correction (FEC) 2108 _(1,2,3), and interleaving 2110_(1,2,3) to their respective input streams. STA1 and STA3 2102 _(1,3),which don't perform channel aggregation, may each apply constellationmapping 2313 _(2,3), inverse discrete Fourier transform (IDFT) 2116_(1,3), guard interval (GI) 2118 _(1,3), and radio frequency frontend(RF) 2120 _(1,3), respectively, to produce channels y₁ and y₃.

STA2 2102 ₂ may use segment parser 2110 ₂ to generate two channels inparallel, and may apply two interleavers 2112 ₂ and 2112 ₂′, twoconstellation mappers 2114 ₂ and 2114 ₂′, two IDFTs 2116 ₂ and 2116 ₂′,two GIs 2118 ₂ and 2118 ₂′, and two RF frontends 2120 ₂ and 2120 ₂′, togenerate two channels y₂ and y₂′.

In FIG. 21, for STA2 2102 ₂, a segment parser 2110 ₂ may be used afterFEC coding 2108 ₂ but before interleaver 2112 ₂. In another example,segment parser 2110 ₂ may follow a single interleaver 2112 ₂ so that itmay achieve better frequency diversity. In another example, the segmentparser 2110 ₂ may be placed before FEC encoder 2108 ₂, where there maybe an FEC encoder for each segment and a separate coding rate and/orcoding scheme may be performed on each segment.

FIG. 22 shows an example PHY layer scheme 2200 with PLCP headers aretransmitted on separate frequency channels. In this example, STA2 (forexample, from FIG. 21) is assigned to channels 218 _(2,3) and may usedata aggregation, STA1 is assigned to channel 218 ₁ and STA3 is assignedto channel 218 ₄. PLCP protocol data units (PPDUs) 2210 _(STA1), 2210_(STA2), 2210 _(STA2)′ and 2210 _(STA3) may be transmitted on theirrespective channels 218 _(1,2,3,4). Each PPDU, for example PPDU 2210_(STA1), may include a preamble portion 2212 _(STA1) and a data portion2208 _(STA1), where the preamble portion 2212 _(STA1) may include ashort training field (STF) 2202 _(STA1), a long training field (LTF)2204 _(STA1), and a signal (SIG) field 2206 _(STA1). Channels 218 _(2,3)may have separate PPDUs 2210 _(STA2) and 2210 _(STA2)′ even though theyare both used by STA2. The SIG fields 2206 _(STA2) and 2206 _(STA2)′ forSTA2 in this example may contain the same information, which may berepeated with or without phase rotation, on channels 218 _(2,3). Withunequal MCS, all MCS may be indicated in the SIG field 2206 _(STA1),2206 _(STA2), 2206 _(STA2)′, and 2206 _(STA3), and mapping between MCSlevels and frequency channels may also be signaled in SIG fields 2206_(STA1), 2206 _(STA2), 2206 _(STA2)′, and 2206 _(STA3). A separate SIGfields 2206 _(STA2) and 2206 _(STA2)′ may be encoded on each channel 218_(2,3) for STA2.

With unequal MCS, each channel 218 _(1 . . . 4) may be assigned aseparate MCS. Therefore, the two SIG fields 2206 _(STA2) and 2206_(STA2)′ transmitted on channels 218 _(2,3) may be different. In anotherexample, the SIG field 2206 _(STA2) for STA2 may be divided into acommon SIG field, and individual SIG fields. The common SIG field maycontain common information for the transmission, and may be transmittedin the SIG fields 2206 _(STA2) and 2206 _(STA2)′ over the channels 218_(2,3). The individual SIG field may contain the information for onefrequency channel/band, for example, the MCS and length field for thechannel/band. The individual SIG field may be transmitted in 2206_(STA2) or 2206 _(STA2)′ on its assigned channel 218 _(2,3),respectively.

Depending on the operation WLAN system, the preamble format 2212_(STA1), 2212 _(STA2), 2212 _(STA2)′, and 2212 _(STA3) may be different.Form example, a longer preamble, including (very) high throughputpreamble or directional preamble for beamforming or MU-MIMOtransmission, may be applied. If the aggregated channels assigned to aSTA are contiguous, the STA or AP may utilize the same transmissionscheme as with non-contiguous aggregation, or operate with widerbandwidth.

FIG. 23 shows an example of DL transmission flow diagram 2300 at an APover hybrid aggregated channels. In the examples of FIGS. 23, 24 and 25,it is assumed channels 1 and 4 are non-contiguous, while channels 2 and3 are adjacent or contiguous. Three MU-PCA STAs 2302 _(1,2,3) maytransmit simultaneously. PPDUs for MU-PCA STAs 2302 _(1,3) may betransmitted on channels 1 and 4 respectively, while STA 2302 ₂ may becapable of channel aggregation and assigned to two contiguous channels,channels 2 and 3, hence transmitting on a larger bandwidth.

Each MU-PCA STA 2302 _(1,2,3) may receive data x₁, x₂, and x₃(respectively) as input and may apply padding 2304 _(1,2,3) as needed tothe data. Each MU-PCA STA 2302 _(1,2,3) may apply scrambling 2306_(1,2,3), FEC 2308 _(1,2,3), interleaving 2310 _(1,2,3), andconstellation mapping 2312 _(2,3) to their respective input streams.MU-PCA STAB 2302 _(1,3), which don't perform channel aggregation, mayeach apply IDFT 2320 _(1,3), GI 2322 _(1,3), and RF 2324 _(1,3),respectively, to produce signals y₁ and y₃. Because STA2 2302 ₂ may usechannel aggregation, STA2 2302 ₂ may apply two IDFTs 2320 ₂ and 2320 ₂′,two GIs 2322 ₂ and 2322 ₂′, and two RF frontends 2324 ₂ and 2324 ₂′, togenerate two signals y₂ and y₂′.

For STA2 2302 ₂, padding bits 2304 ₂ may be added to the input streamx₂, and then pass to the scrambler 2306 ₂. The scrambled bits areforwarded to the FEC 2308 ₂ for FEC coding. An interleaver 2310 _(STA2)may be applied and the interleaved bits may be passed to theconstellation mapping 2312 _(STA2). The constellation symbols generatedmay be passed to a space time coding block (STBC) 2314. In an example,the constellation symbols may be passed directly to spatial mapping unit2318 without the STBC 2314. STBC 2314 may be specified in the TXVECTORpassed from MAC layer to PHY layer and this information may betransmitted in a SIG field. After the STBC block 2314, one symbol streammay become two symbol streams 2325 and 2325′. The first symbol stream2325 may be passed as it is to the spatial mapping unit 2318, and thesecond symbol stream 2325′ may be applied with a cyclic shift diversity(CSD) scheme 2316. A spatial mapping unit 2318 may be applied on the twosymbol streams 2325 and 2325′. The spatial mapping unit 2318 may be, forexample, a spatial domain precoding scheme. Then general IDFT 2320 ₂ and2320 ₂′, GI blocks 2322 ₂ and 2322 ₂′, and RF frontend 2324 ₂′ arefollowed for each symbol stream.

The IDFT 2320 ₂ and 2320 ₂′ sizes utilized by STA 2302 ₂ in this examplemay be two times larger than the size of the IDFTs 2320 _(1,3) of MU-PCASTAs 2302 _(1,3). Additionally, different transmission schemes may beapplied to STA 2302 ₂. For example, any of the following transmissiontechniques may or may not be used: space-time block coding (STBC) 2314,beamforming (not shown), or other MIMO schemes not shown may beutilized. Cyclic Shift Diversity (CSD) 2316 may be used to applyprogressive phase or time shifts to each spatial stream, which mayincrease the frequency diversity of the channel for MU-PCA. Spatialmapping unit 2318 may be used to map the coded information to separatespatial streams. Moreover, both equal MCS and unequal MCS schemes may beapplied. With unequal MCS, an extra segment parser may be applied tosplit the MAC packet. There are many possible ways to split the packet.For example, a packet may be split into two parts, where each part iscorresponding to a different channel (e.g. channels 2 and 3).

In another example, the packet may be split into more than two parts andeach part may correspond to predefined sub-channels or sub resourceblocks, where resource block may refer to a group of subcarriers. Aresource block may be smaller than or equal to a sub-channel. DifferentMCS levels may be applied to different parts, such that the MCS levelsmay be signaled in the SIG field. A SIG field may include all the MCSlevels for a user. The mapping between MCS levels and channels/resourceblocks may also be given in the SIG field. The SIG field may be repeatedover all the channels or the SIG field may be divided into a common SIGfield, and an individual SIG fields. The common SIG field may containcommon information for the transmission, and may be transmitted over allavailable channels. The individual SIG field may contain the informationfor one frequency channel/band, for example, the MCS and length fieldfor the channel/band. The individual SIG field may be transmitted on thechannel/band to which it is assigned.

When a STA aggregates multiple channels (contiguous or non-contiguous),it may interleave, with a single interleaver, over all channels, andalso use unequal MCS. One way to accomplish this is as follows. LetN_(BITS) be the total number of bits to be transmitted in one aggregatedorthogonal frequency division multiplexing (OFDM) symbol. N_(BITS) maydepend on the desired constellation in each band denoted by a number ofbits per constellation symbol N_(BPS,i) and a number of data carriers(N_(D,i)) in each band i as follows:

$\begin{matrix}{N_{BITS} = {\sum\limits_{i}{N_{D,i}N_{{BPS},i}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

For example, in 802.11a 40 MHz channel has N_(D,1)=108 whereas a 20 MHzchannel has N_(D,2)=52. If one 40 MHz and one 20 MHz channel were to beaggregated, with the 40 MHz mode being used with 64 QAM (N_(BPS,1)=6 andN_(D,1)=108) and the 20 MHz mode with 16 QAM (N_(BPS,2)=4 andN_(D,2)=52), then N_(BITS)=108×6+52×4=856. Then, the number of columns(N_(COL)) may be set for the interleaver based on N_(BITS). N_(COL) maybe a factor of N_(BITS). Continuing the example above, N_(COL) may be 8or 107, where 856=8×107. N_(COL) may be derived from simulation resultsfor the particular channel model. The number of rows in the interleavermay be defined as N_(ROW)=N_(BITS)/N_(COL). The index of the coded bitbefore the first permutation may be denoted by k; i may be the indexafter the first and before the second permutation; and j may be theindex after the second permutation, just prior to modulation mapping.Accordingly, the first permutation of the interleaver may be defined as:i=N _(ROW)(k mod N _(COL))+floor(k/N _(COL)) k=0,1, . . . ,N_(BITS)−1  Equation 2

The second permutation may be carried out on each band separately,depending on the MCS being used in that band. AssumeN_(TOT,i)=N_(D,i)N_(BPS,i) denotes the number of total bits in each bandper OFDM symbol. Then:

$\begin{matrix}{\mspace{79mu}{{s_{i} = {\max\left( {\frac{N_{{BPS},i}}{2},1} \right)}}\mspace{20mu}{and}}} & {{Equation}\mspace{14mu} 3} \\{{j = {{s_{i} \cdot {{floor}\left( {k/s_{i}} \right)}} + {\left( {k + N_{{TOT},i} - {{floor}\left( {N_{COL},\frac{k}{N_{{TOT},i}}} \right)}} \right){mod}\; s_{i}}}}\mspace{20mu}{{k = 0},1,{N_{{TOT},i} - 1}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

When there are multiple spatial stream, the interleaver described abovemaybe used on each spatial stream, and an additional rotation may beapplied between different spatial streams. A deinterleaver may reversethe above permutations on each band and spatial stream, if present.

FIG. 24 shows an example flow 2400 of PPDU transmissions over channelsincluding hybrid aggregated channels. Assuming STA1, STA2, and STA3 fromFIG. 23 are transmitting PPDUs 2401 _(STA1), 2401 _(STA2), and 2401_(STA3), PPDUs 2401 _(STA1) and 2401 _(STA3) for STA1 and STA 3 may betransmitted on channels 218 ₁ and 218 ₄ respectively, while STA2 may becapable of channel aggregation and assigned to two contiguous channels218 _(1,2), hence transmitting on a larger bandwidth. PPDUs 2401 _(STA1)and 2401 _(STA3) may include, respectively: STF 2402 _(STA1) and 2402_(STA3), LTF 2404 _(STA1) and 2404 _(STA3), SIG 2406 _(STA1) and 2406_(STA3) and data (plus padding) 2408 _(STA1) and 2408 _(STA3). STF maybe used for starting of packet detection, and coarse time and frequencyoffset correction, among other things. LTF may be used for fine time andfrequency offset correction, and channel estimation, among other things.SIG field may carry the PHY layer header.

PPDU 2401 _(STA2), which includes aggregated data transmitted over twochannels 218 _(2,3), may include: STF 2402 _(STA2), LTF 2404 _(STA2) andLTF 2410 _(STA2), SIG 2406 _(STA2) and data (plus padding) 2408 _(STA2).PPDU 2401 _(STA2) may have two LTFs 2404 _(STA2) and 2410 _(STA2), wherethe second LTF 2410 _(STA2) may be used for channel estimation if twodata streams are transmitted to STA2.

Comparing to PPDUs 2401 _(STA1) and 2401 _(STA3) for STA1 and STA3,which are transmitted with normal bandwidth, in the PPDU 2401 _(STA2)for STA2, both the PLCP header including STF 2402 _(STA2), LTF 2404_(STA2), SIG field 2406 _(STA2), and data 2408 _(STA2) for STA2 aretransmitted with wider bandwidth. Transmissions shown in this exampleflow 2400 may be protected by GRTS/GCTS protocol. Therefore unintendedSTAs in the same BSS or overlapping BSS (OBSS) may not need tounderstand the MU-PCA transmission. In the example of FIG. 24,unintended STAs may not understand the preamble transmitted on channel218 _(2,3) if they are not capable to operate on a wider bandwidth. Theunintended STAs may detect GRTS/GCTS sequence transmitted before thedata session, and set NAV accordingly. However, it is also possible toprovide extra protection at the PHY layer by changing PLCP headerformat.

FIG. 25 shows another example flow 2500 of PPDU transmissions overchannels including hybrid aggregated channels. The transmission schemeover the channels 218 _(1 . . . 4) is the same as in FIG. 24 (PPDU 2501_(STA1) is the same as PPDU 2401 _(STA1), PPDU 2501 _(STA2) is the sameas PPDU 4501 _(STA2), and PPDU 2501 _(STA13) is the same as PPDU 2401_(STA3)) except for the legacy PLCP header information for STA2 that maybe transmitted separately on channels 218 _(2,3). The legacy PLCP headerinformation includes: legacy STF (LSTF) 2502 _(STA2), legacy LTF (LLTF)2504 _(STA2) and legacy SIG (LSIG) 2506 _(STA2). Therefore, FIG. 25shows an example variation of PLCP header format to FIG. 24, which maybe detectable by non MU-PCA users and other OBSS users since one set ofSTF, LTF and SIG field is transmitted repeatedly on channel 2 andchannel 3.

The above examples described in FIGS. 23-25 show a solution tocommunicate with STA2/User 2 with wider bandwidth. System spectralefficiency may be higher when using wider bandwidth, therefore ascheduler may be aware of whether channel aggregation is donecontiguously or not, and may try to assign users with heavy traffic loadto the contiguously aggregated channels. In another example, STA2/User 2may communicate with the normal single channel bandwidth but occupy twonormal channels. The IFFT/IDFT size for STA2/User 2 may be the same asthat for STA1 and STA3. In this case, a segment parser may be utilizedto split the traffic to two parts (similar to the examples of FIGS. 21and 22). Depending on the channel quality and STA feedback capability,both equal MCS and unequal MCS may be applied. This solution may be lessefficient than the STA2/User 2 operating with wider bandwidth), but maybe easier to implement.

In one example, a STA may be capable of MIMO. MIMO scheme may be usedfor MU-PCA transmissions. MIMO transmission may include, but is notlimited to, space division multiplexing (SDM), STBC, beamforming, CDD,or MU-MIMO. MIMO transmission may depend on the number of availableantennas at the transmitter and receiver sides. For example, a MIMOsystem with M transmit antennas and N receive antennas may support up tomin(M,N) spatial data streams either for single users MIMO (SU-MIMO) orMU-MIMO. In existing WiFi specifications and standards, AP/STA may haveknowledge of the number of available antennas at the both thetransmitter and receiver sides. Thus, an appropriate MIMO scheme may beselected. In MU-PCA transmission, knowing the number of antennasavailable at AP side may not be enough for STA to choose a proper MIMOscheme since the antennas at AP side need to be shared with multipleusers. Moreover, the number of users supported by MU-PCA transmissionmay change from time to time. Therefore, it may not be possible for theAP to announce its MIMO capability and number of supported MU-PCA usersonce, and all the MU-PCA transmissions may follow the same setup. In anexample, the AP may assign the MCS to the STAs. In this way, the AP maydetermine the proper MIMO scheme for STAs, and may announce MCS andmultiple user positions (which define channel/spatial stream assignmentfor multiple users) in, for example, the PLCP header (e.g. in the SIGfield). In another example, this information may be exchanged prior tothe MU-PCA transmission.

In another example of STA behavior, a STA may not be capable of channelaggregation. In this case, the STA may be assigned a maximum of onechannel, and one bandwidth. MU-PCA or SU-PCA may utilize the sametransceiver scheme. Both equal MCS and unequal MCS may be applied, anddifferent MIMO schemes may be applied as well.

When a set of channels are used in either SU-PCA or MU-PCA, the transmitpower used for each channel may be different. This may be due toregulations established by regional or national administrations or dueto channel conditions observed that may be vastly different. In theSU-PCA case, the channels in the aggregated channel set may experiencedifferent interference, fading, etc. In the MU-PCA case, the channelsbetween the AP and the various STAs may vary due to distance, shadowfading, etc., in addition to interference and fast fading. Unequal MCSsmay be used to accommodate the conditions of each channel and to achievehigher throughput.

In order to support unequal MCSs and/or unequal transmit powers for eachof the set of contiguous or non-contiguous channels or frequencysegments, modified TXVECTOR and RXVECTOR may be used, examples of whichare described in the following. The TXVECTOR and RXVECTOR may bedesigned as vectors in the following form:TXVECTOR=[TXVECTOR_Common,TXVECTOR_0,TXVECTOR_1, . . .,TXVECTOR_N]  Equation 5RXVECTOR=[RXVECTOR_Common,RXVECTOR_0,RXVECTOR_1, . . . ,RXVECTOR_N]  Equation 6where TXVECTOR_Common and RXVECTOR_Common may contain parameters thatapply to all channels used in the SU-PCA or MU-PCA or all frequencysegments; and TXVECTOR_i and RX_VECTOR_i, for 0≦i≦N, may containparameters specific to the i^(th) channel or frequency segment. Thei^(th) channel may be of any bandwidth and may consist of contiguous andnon-contiguous frequency segments.

For example, in 802.11af networks, TXVECTOR_i and RXVECTOR_i may containparameters for the i^(th) channel of bandwidth W, for example, inoperation modes defined in the 802.11af standard such as TVHT_W,TVHT_2W, TVHT_4W, TVHT_W+W and TVHT_2W+2W operation modes.

Alternatively, TXVECTOR_i and RXVECTOR_i may contain parameters for thei^(th) channel of bandwidth 2W in the TVHT_2W, TVHT_4W and TVHT_2W+2Woperation modes. Some parameters that may be included in theTXVECTOR_Common and RXVECTOR_Common are shown in Table 5, where Y and Nindicate the presence (Y) or absence (N) of the corresponding parameter.

TABLE 5 Parameter Description TXVECTOR_Common RXVECTOR_Common Format VHTindicates VHT Format Y Y TVHT indicates TVHT Format NON_HT_ModulationSimilar to 11AC settings Y Y N_TX Total Number of transmit Y N chainsCH_Bandwidth Indicates the bandwidth of the Y Y SU-PCA and MU-PCAtransmissions.

Table 6 shows some parameters that may be included in the TXVECTOR_i andRXVECTOR_i where Y and N indicate the presence (Y) or absence (N) of thecorresponding parameter in TXVECTOR_i and RXVECTOR_i, and MU indicatespresence for MIMO mode.

TABLE 6 TX- RX- Parameter Description VECTOR VECTOR N_TX_i Total Numberof transmit chains used for the i^(th) Y N channel or frequency segmentCH_Bandwidth_i The bandwidth for the i^(th) channel or frequency Y Ysegment. For example, CH_Bandwidth_i may be W, W + W, 2W, 2W + 2W and 4Win 802.11af. EXPANSION_MAT_TYPE_i It may be set to Compressed_SV for thei^(th) Y N channel or frequency segment EXPANSION_MAT_i Contains a setof beamforming feedback matrices MU N for the i^(th) channel orfrequency segment CHAN_MAT_TYPE_i It may be set to Compressed_SV for theN Y i^(th) channel or frequency segment CHAN_MAT_i Contains a set ofcompressed beamforming N Y feedback matrices based on the channelmeasured during the training symbols of the received PPDU on the i^(th)channel or frequency segment DELTA_SNR_i Contains a set of delta SNRvalues based MU Y on the channel measured during the training symbols ofthe received PPDU RCPI_i Measured received RF power on the i^(th)channel N Y or frequency segment SNR_i Measured SNR_i per spatial streamon N Y the i^(th) channel or frequency segment FEC_CODING_i Indicateswhich FEC encoding is used MU MU on the i^(th) channel or frequencysegment STBC_i Indicates whether STBC is used on the i^(th) Y Y channelor frequency segment TXPWR_Level_i Indicates the transmit output powerlevels that Y N shall be used for the current transmission on the i^(th)channel or frequency segment RSSI_i Measured RSSI value for the i^(th)channel or N Y frequency segment MCS_i The MCS scheme used for thetransmission Y N of the PPDU REC_MCS_i Indicates the MCS that the STA'sreceiver N Y recommends PSDU_Length_i Indicates the number of octets inthe PSUD N Y on the i^(th) channel or frequency segment USER_POSITION_iIndex for user in MU transmission on the i^(th) N Y channel or frequencysegment NUM_STS_i Indicates the number of space-time streams MU Y on thei^(th) channel or frequency segment GROUP_ID_i Indicates the Group_ID onthe i^(th) channel or Y Y frequency segment Partial_AID_i Abbreviatedindication of the intended Y Y recipient(s) on the i^(th) channel orfrequency segment NUM_USERS_i Indicates the number of users on thei^(th) channel Y N or frequency segment BEAMFORMED_i Set to 1 if abeamforming steering matrix is Y Y applied to the waveform in a SUtransmission

All parameters in Table 6, for example Parameter_i, for 0≦i≦N, may be aparameter specific to the i^(th) channel or frequency segment. Thei^(th) channel may be of any bandwidth and may consist of contiguous andnon-contiguous frequency segments. For example, in 802.11af networks,Parameter_i may be a parameter for the i^(th) channel of bandwidth W ina TVHT_W, TVHT_2W, TVHT_4W, TVHT_W+W and TVHT_2W+2W operation mode.Alternatively, Parameter_i may be a parameter for the i^(th) channel ofbandwidth 2W in the TVHT_2W, TVHT_4W and TVHT_2W+2W operation mode.

The STA/AP may achieve the support for unequal MCS and unequal transmitpower for SU-PCA and MU-PCA by using PLCP transmit and receiveprocedure, such as the examples discussed below, and the STA/AP mayobtain access to the channel as described in above. Transmission of thePPDU may be initiated by the PLCP after receiving the PHYTXSTART.request(TXVECTOR) primitive, such that the TXVECTOR elements for thePHY-TXSTART.request primitive are described above.

For each channel or frequency segment, the PLCP may issue the parametersin the following physical medium dependent (PMD) primitives to configurethe PMD: PMD_TXPWRLVL.request and PMD_TX_PARAMETERS.request. TheTXPPWRLVL and TX_PARAMETERS may be specific for each of the channel orfrequency segment. The PLCP may issue a PMD_TXSTART(TXVECTOR).requestprimitive to start transmission of a PLCP preamble on each of thechannels or frequency segments defined by the elements in the TXVECTORparameter. After the PLCP preamble transmissions are started on allchannels or frequency segments, the PHY layer entity may initiate datascrambling and data encoding. The encoding method for the Data field ofeach packet on each channel or frequency segment may be based on theFEC_CODING_i, CH_BANDWIDTH_i, NUM_STS_i, STBC_i, MCS_i, and NUM_USERS_iparameter of the TXVECTOR, as described above. The data may be exchangedbetween the MAC and PHY layers through a series ofPHY-DATA.request(DATA) primitives for each data frame on each of thechannels or frequency segments issued by the MAC, and PHY-DATA.confirmprimitives issued by the PHY layer.

PLCP receive procedures may support unequal MCS and unequal transmitpower in SU-PCA and MU-PCA. Upon the PMD receiving the transmitted PLCPpreambles on all channels or frequency segments, PMD_RSSI.indication mayreport a receive signal strength to the PLCP for each of the channels orfrequency segments. The PMD primitive PMD_RSSI may be issued to thePLCP, which may record a received RSSI value, RSSI-i, for each of thechannel or frequency segment. The PLCP may include the most recentlyreceived RSSI_i values in the PHY-RXSTART.indication(RXVECTOR) primitiveissued to the MAC.

After the PHY-CCA.indication(BUSY, channel-list) is issued, the PHYentity may begin receiving the training symbols on all the channels orfrequency segments. A PHY-RXSTART.indication(RXVECTOR) primitive may beissued when correct signaling and modes are detected from the preambleson all the channels or frequency segments. The RXVECTOR associated withthis primitive may include any of the parameters specified above. ThyPHY layer may further decode the PSDUs on all the channels or frequencysegments according to the RXVECTOR. The received bits for the PSDUs maybe assembled into octets, decoded, and presented to the MAC using aseries of PHYDATA.indication(DATA) primitive exchanges for each PSUD ona channel or frequency segment. After the reception of the final bit ofthe last PSDU octet, and possible padding and tail bits, on all channelsor frequency segments, the receiver may return to the RX IDLE state.

The PHY layer may have some limitations on operation bandwidth. Forexample, some of the 802.11ah devices, when participate in MU-PCA, maybe able to aggregate multiple channels, however, the bandwidth of eachoperation channel may be limited to 2 MHz, while at the AP side, threechannels (each with bandwidth 1 MHz) may be aggregated and assigned tothis MU-PCA user. In this example, at the MAC layer, the AP may preparetwo separate MAC packets, which will be transmitted to the user. At thePHY layer, the AP may assign one MAC packet to one of the aggregatedchannels, with 2 MHz bandwidth, and may assign the rest of MAC packet toanother channel with 1 MHz bandwidth. This may be achieved using layermapping.

FIG. 26 is a flow diagram of an example method 2600 of using layermapping 2604 to map N MAC packets 2602 (for N or fewer users) to Klayers 2606. Each layer may process the assigned data streamindependently. For example, each layer may have separate coding andmodulation schemes, also separate MIMO schemes. Different interleavers(not shown) may be defined for each layer or one interleaver may be usedover several layers. The layer mapping 2604 may, for example: map oneMAC packet to one layer; multiple MAC packets to one Layer; one MACpacket to multiple layers; or comprehensive mapping from multiple MACpackets to multiple layers. After layer processing, the packet may bepassed to Spatial/Frequency Mapping 2608, which may further map themultiple layers to multiple spatial streams or frequency bands. Themethod 2600 may be applied to all the PHY designs discussed previously.

The following examples, pertain to MU-PCA enabled by usingtransmit/receive with asymmetrical bandwidth. Using asymmetricalbandwidth may have a flexible architecture, and the number of users itmay support by MU-PCA is not limited by the number of antennas.Moreover, it may simplify or reduce the cost of the WLAN STA, or AP/STAdesign. Use of MU-PCA over contiguous and/or non-contiguous channelsthrough widely separated frequencies may be challenging for asymmetricalbandwidth. For example, UL MU-PCA STAs transmitted simultaneously to theAP may have to be close in received power levels at the AP in order toavoid the near-far problem. Also, simultaneous transmission of UL MU-PCApackets may have to arrive at the AP within the Guard Interval (GI) toallow the AP to correctly decode each packet.

The 802.11af and 802.11ah specifications may be considered clocked downversions of the 802.11ac specification. Consequently, the guard interval(GI) may become as long as 8 microseconds, which may be sufficientlylong to allow time alignment of UL MU-PCA packets assuming a Round TripTime (RTT) of 6.67 microseconds over a coverage range of 1 km. It isalso noted that the Timing Synchronization Function (TSF) timer mayretain its current precision of 1 microsecond. Under the assumption ofTSF timer precision and GI durations, a single receiver may be used atthe AP, instead of multiple receiver for each of the frequency segments,to receive packets from multiple STAs simultaneously.

The channelization proposed in the 802.11ah framework may make the useof transmit/receive with asymmetrical bandwidth a reasonablepossibility. It is possible for current, and near future, RF techniquesto cover the entire bandwidth envisioned for 802.11ah and other sub-1GHz technologies with a single RF chain.

MAC and PHY layer methods leverage the above observations to handletransmit/receive with asymmetrical bandwidth. The MAC Layer schemes forstandalone UL, standalone DL, combined UL/DL and retransmission schemesmay be similar to those described above for transmit/receive withasymmetrical bandwidth. However, since transmit/receive are withasymmetrical bandwidth, additional modifications of the MAC Layer may beperformed, as described below. PHY Layer methods for supporting MU-PCAwith asymmetrical bandwidth are also presented. One example is toprovide MU-PCA using a relatively wideband AP and relatively narrowbandSTAs. In another example, MU-PCA is provided to STAs using amulti-narrow band combined AP and narrowband STAs. In these examples,the hardware of the AP and the non-AP may be modified.

Examples methods, signaling and procedures described below provideMU-PCA for multiple STAs simultaneously over multiple contiguous, ornon-contiguous, channels of widely separated frequencies. These methodsmay enable MU-PCA using transmit/receive with asymmetrical bandwidth in,for example, 802.11ah, or similar technologies, and it may also enableMU-PCA in other WLAN systems where there is precise timing to align ULMU-PCA transmissions.

The MAC designs to support MU-PCA using transmit/receive withasymmetrical bandwidth may consist of two parts, discussed below: theMAC schemes that enable standalone DL, standalone UL and combined DL/ULMU-PCA; and STA group management. The MAC Layer schemes for standaloneUL, standalone DL, combined UL/DL, UL/DL MU-PCA and retransmissionschemes are similar to those presented in the case of MU-PCA usingtransmit/receive with symmetrical bandwidth as discussed above.

STAs participating in the MU-PCA (using transmit/receive withasymmetrical bandwidth) may be organized into groups in a pre-arrangedor ad hoc fashion for UL, DL or combined UL and DL transmissions. TheSTA grouping for UL and DL may be different. The DL MU-PCA groupmanagement is similar to that described above for MU-PCA usingtransmit/receive with symmetrical bandwidth. The STAs may be groupedtogether according to one or combination of several different criteriasuch as operating channel width, similar received power at the AP, QoSpriorities, synchronizations, and buffered packet length, among othercriteria. If coordinated well, the group of STAs may be able to utilizesome portion of the available frequency bandwidth up to the entirebandwidth.

For UL MU-PCA group management, simultaneous UL MU-PCA transmissions mayarrive at the AP with similar receive power and within the GI. Thegrouping may be conducted using the received signal strength indication(RSSI) indicator for each STA that may already be available to the AP.The AP may record the RSSI for each packet received from a STA. The APmay define RSSI intervals in the form of, for example, [0 dB, N dB],[N+1 dB, 2×N dB], . . . , [m×N+1 dB, (m+1)×N dB]. The value of N maydepend on the tolerance of the receiver of the AP. For example, a STAmay fall in RSSI interval or bin n if 90% of its latest L RSSI valuesfall into the interval [(n−1)×N+1 dB, n×N dB].

All STAs contained in the same bin may be candidates to be grouped intothe same UL MU-PCA group. Since RSSI may be a coarse estimation of thedistance between the STA and AP, it may allow simultaneously transmittedUL MU-PCA packets from the group to arrive at the AP within the GI. STAswithin the same RSSI bin may be further selected into groups that maymaximally occupy available channels by diverse criteria, for example, bydoing any of the following: selecting STAs of the maximal channel widthfirst; selecting STAs of the minimal channel width first; or selectingSTAs with similar QoS requirements. In addition, a variety of signaling,mechanisms and procedures for grouping of STAs as well as for groupmonitoring and maintenance may be applied to enable MU-PCA in a varietyof WLAN systems.

PHY layer procedures for MU-PCA using transmit/receive with asymmetricalbandwidth are described in the following. In some cases, the AP mayperform relatively wideband transmit/receive, and a STA may performrelatively narrowband transmit/receive. PHY layer methods may lower thehardware cost at the AP side, may increase the complexity at the STAside, and/or may make the MU-PCA more flexible. Assuming OFDM based WLANsystems, for different channel bandwidth, the subcarrier frequencyspacing may be a constant number. Accordingly, once the channelbandwidth is doubled, the IFFT/FFT size utilized for the OFDM system mayalso doubled. For example, in 802.11ah, the 2 MHz channel bandwidth modemay require a 64 point IFFT/FFT at the PHY layer, while the 4 MHzchannel bandwidth mode may require a 128 point IFFT/FFT. Assumesub-carrier spacing is denoted as Δ_(F).

Assuming the AP has aggregated N channels, and each channel has centerfrequency f_(n), nε{1, 2, . . . N} and bandwidth BW_(n), then theaggregated channel bandwidth BW may be:

$\begin{matrix}{{BW} = {\sum\limits_{n = 1}^{N}{BW}_{n}}} & {{Equation}\mspace{14mu} 7}\end{matrix}$

The bandwidth spanned by the entire aggregation is:

$\begin{matrix}{{BW}_{span} = {{\max\left( {{f_{1} + \frac{{BW}_{1}}{2}},\ldots\mspace{14mu},{f_{n} + \frac{{BW}_{N}}{2}}} \right)} - {\min\left( {{f_{1} - \frac{{BW}_{1}}{2}},\ldots\mspace{14mu},{f_{N} - \frac{{BW}_{N}}{2}}} \right)}}} & {{Equation}\mspace{14mu} 8}\end{matrix}$

For contiguous channel aggregation, BW=BW_(span), whereas fornon-contiguous channel aggregation case, BW<BW_(span). The AP may assignthe aggregated channels to K users. The IFFT/IDFT size N_(FFT) utilizedat the aggregated channel may be equal to:

$\begin{matrix}{N_{FFT} = {{round}\left( \frac{{BW}_{span}}{\Delta_{F}} \right)}} & {{Equation}\mspace{14mu} 9}\end{matrix}$For example, in 802.11ah, if the AP contiguously aggregates two 1 MHzchannels and one 2 MHz channel, then BW=BW_(span)=4 MHz. If Δ_(F)=31.25kHz, then the IFFT/IDFT size N_(FFT) for the aggregated channel is4000/31.25=128. In an example with non-contiguous channel aggregation,BW_(span)=5 MHz, while BW=4 MHz, and the IFFT/IDFT size N_(FFT) for thisnon-contiguously aggregated channel is 5000/31.25=160.

PPDU structure and PLCP header may be modified, as illustrated in FIGS.27, 28 and 29. In FIGS. 27, 28, and 29, the PLCP header includes shorttraining field (STF), long training field (LTF) and SIG field. A PLCPheader may include a longer preamble, for example, it may include: afirst set of STF, LTF, SIG fields for legacy operation or for Omnioperation where the set of STF, LTF, SIG may be transmitted with Omniantenna weight); and a second set of STF, LTF and SIG field for (very)high throughput operation or directional operation, where the set ofSTF, LTF, SIG may be transmitted with selected antenna weight, and wherethis mode may be used for MU-MIMO transmission or Beamformingtransmission. The DL and UL transceiver s are described below.

For the DL transmitter, the STF could be transmitted using STF format ofthe smallest channel defined in the standards. In different parallelchannels, the STF may be repeated with or without phase rotation. Inanother example, the STF may be transmitted using the same bandwidth asthe rest of packet. LTF, SIG and Data fields may be transmitted usingthe IFFT/IDFT size N_(FFT) as defined in Equation 9. Special guardintervals and/or null subcarriers (tones) may be inserted between users.The special guard/null subcarriers may be designed according tocorresponding spectral mask requirements. The location of guard/nulltones may be changed according to the user allocation and userbandwidth. LTF may be transmitted using wideband format with the guardtones. LTF may be used with narrow band format; however, the LTFsequence may cover all the data subcarriers utilized in SIG/Data portionof the packet. The SIG field may be identical and repeated on eachchannel; or it could be user specific or channel specific.

FIGS. 27 and 28 show examples of PHY layer schemes 2700 and 2800 with 3and 2 MU-PCA users, respectively. In FIG. 27, STA1 is assigned tochannel 218 ₁, STA3 is assigned to channels 218 _(2,3), and STA4 isassigned to channel 218 ₄. The AP may transmit STF 2702 _(AP) with orwithout phase rotation over each aggregated channel 218 _(1 . . . 4),followed by LTF 2704 _(AP), while transmitting LTF 2704 _(AP) over thecombined bandwidth of channels 218 _(2,3). The STAs (STA1, STA3, andSTA4) may transmit Sig 2706 _(STA1), 2706 _(STA3), and 2706 _(STA4), anddata (and padding) 2708 _(STA1), 2708 _(STA3), and 2708 _(STA4) to theAP over their respectively assigned channels.

In FIG. 28, STA1 is assigned to channels 218 _(1,2), and STA2 isassigned to channels 218 _(3,4). The AP may transmit STF 2702 _(AP) withor without phase rotation over each aggregated channel 218 _(1 . . . 4),followed by LTF 2804 _(AP) over the combined bandwidth of channels 218_(1,2) and 218 _(3,4). The STAs (STA1, STA3, and STA4) transmit SIG 2806_(STA1) and 2806 _(STA2) and data (and padding) 2808 _(STA1) and 2808_(STA2) over their respectively assigned channels.

FIG. 29 shows an example of a PHY layer scheme 2900 with an example STFformat for MU-PCA transmissions. In FIG. 29, STA1 is assigned tochannels 218 _(1,2), and STA2 is assigned to channels 218 _(3,4). TheSTF 2902 _(AP) may be transmitted using the same bandwidth as the restof the packet, that is over combined channels 218 _(1,2) and 218 _(3,4).Simple or preamble format may be used. For example, the long preamblewith (very) high throughput portion or directional portion (used forBeamforming or MU-MIMO transmission) may be used. The long preamble mayprovide extra PHY protection. As in the example of FIG. 28, the AP maytransmit LTF 2904 _(AP) over the combined bandwidth of channels 218_(1,2) and 218 _(3,4). The STAs (STA1, STA3, and STA4) may transmit SIG2906 _(STA1) and 2906 _(STA2) and data (and padding) 2908 _(STA1) and2908 _(STA2) over their respectively assigned channels.

FIG. 30 shows an example PHY layer scheme 3000 with PPDUs using longpreamble to provide extra protection over MU-PCA transmissions. Anarrowband transmission 3002 by the AP, including the preamble portionincluding STF 3006 _(AP), LTF 3008 _(AP), and SIG field 301 _(0AP), maybe repeated on each channel 218 _(1 . . . 4). The preamble portioncorresponding with narrowband transmission 3002 may be detected bynormal unintended STAs with or without MU-PCA capability. A preambleportion corresponding to the MU-PCA transmission 3004, including STF3012 _(AP) and LTF 3014 _(AP), may be detected by MU-PCA capable STAs.The STAs in the MU-PCA group (STA1, STA3 and STA4) may respectivelytransmit SIG fields 3016 _(STA1), 3016 _(STA3), and 3016 _(STA4) andtheir data (with padding) 3018 _(STA1), 3018 _(STA3), and 3018 _(STA4).Information may be carried in the SIG fields 3010 _(AP) of thenarrowband transmission, such that non MU-PCA capable STAs or unintendedSTAs may know it is a MU-PCA transmission, and if it is a potentialdestination or receiver of the MU-PCA transmission. Other variations arepossible. For example, MU-PCA STF 3012 _(AP) and LTF 3014 _(AP)transmission may be omitted, and the legacy STF (LSTF) and legacy (LLTF)may be reused.

In FIGS. 27-30, the LTFs 3014 _(AP) are shown with the same length orduration among all the MU-PCA users. This is referred to as equal LTFdesign. With equal LTF design, the AP may know the number of datastreams assigned to each MU-PCA users, thus the number of LTF symbolsused for channel estimation for each MU-PCA user may be calculatedaccordingly. The AP may transmit the LTF with the largest number amongall the MU-PCA users. For example, STA1 may transmit one data stream,thus one LTF may be used for channel estimation. STA2 may transmit twodata stream, thus two LTFs may be used for channel estimation. ForMU-PCA for STA1 and STA2 together, the AP may transmit 2 LTFs. In thisway, the AP may signal each user the number of data streams it assignedand the number of total LTFs transmitted in SIG field.

In another example, unequal LTF may be used. With this design, the APmay transmit the number of LTFs needed for that user. Using the aboveexample again, the AP may transmit one LTF for STA1 on its assignedchannel(s), which may be followed by the transmission of data. The APmay transmit two LTFs for STA2 on its assigned channel(s). In this way,the AP may signal each user the number of data streams assigned.

FIG. 31 shows an example transmission flow diagram 3100 at the AP side.Layer may correspond to data stream, MAC packet, users or other possiblepartition of data. Following layer mapping 3102, each of the M layers3104 _(1 . . . M) may be separately coded and modulated using separatelayer processing. In another word, each layer may have its own MCS andMIMO schemes. In FIG. 31, each layer 3104 _(1 . . . M) may include, forexample: padding component 3106 _(1 . . . M), scrambler 3108_(1 . . . M), FEC component 3110 _(1 . . . M), interleaver 3112_(1 . . . M), constellation mapper 3114 _(1 . . . M), STBC 3116_(1 . . . M), and multiple cyclic shift diversity (CSD) components 3118_(1 . . . M). In an example, the PHY layer may split a MAC packet intomultiple layers, for a one user case where one MAC packet is preparedfor unicast to the user. Frequency segment mapper 3120 may map the Mlayers to the K frequency segments or channels, and each segment may beprocessed with IDFT 3122 _(1 . . . K), and a GI components 3124_(1 . . . K) may apply guard intervals between users.

For example, multiple MAC packets may be prepared, such that each usermay have one MAC packet or multiple MAC packets. The AP may map the MACpackets to multiple layers, by mapping multiple MAC packets to onelayer; or mapping one MAC packet to multiple layers. Coding andmodulation may be performed on each layer, then frequency segmentmapping may map the layers to frequency segments. Multiple layers may bemapped to one frequency segment, or one layer may be mapped to multiplefrequency segments. In another example, the AP may broadcast ormulticast one MAC packet to multiple users on multiple channels. The MACpacket may be repeatedly mapped to multiple layers then multiplefrequency segments.

For a DL receiver, The STA may need to know the AP transmittingbandwidth (BW_(span)) and the sub-channel allocation. The exchange ofthis information may be done within the MAC handshakes (for example, thegrouping configuration signaling) before the MU-PCA transmission. STAmay use at least the same sampling rate as AP. Instead of using the samewide-band filtering, the STA may apply its narrow band filtering. As fora WiFi signal, the STA may utilize STF(s) on its own frequency band forautomatic gain control (AGC), coarse frequency offset and coarse timingdetection. A wideband FFT with size N_(FFT) may be performed, and basedon truncated or full size LTF (which may depend on whether a widebandLTF or narrow band LTF is transmitted), fine timing frequency correctionand channel estimation may be applied. Following LTF the, SIG field anddata part may be decoded normally. The FFT size used at the STA side maybe N_(FFT) defined in Equation 9.

For an UL transmitter, the STA may need to know the AP receivingbandwidth (BW_(span)) and sub-channel allocation. The exchange of thisinformation may be done within the MAC handshakes (for example, thegrouping configuration signaling) before setting up the MU-PCAtransmission. The STF transmitted by each STA may be a narrow bandformat, while the LTF transmitted by each STA may be a truncatedwideband LTF, or a narrow band format LTF. With a narrow band LTF, theLTF sequence in frequency domain may cover all the data subcarriers bythe corresponding transmitting STA.

FIG. 32 shows an example transmission flow diagram 3200 at the STA side,which may be used to prepare the data portion of PPDU for transmission.One layer, layer 3204 _(m), is shown in FIG. 32, however, more than onelayer may be allocated to the STA, and each layer may have a separateMCS. Following layer mapping 3202, layer 3204 _(m) may apply any of thefollowing to the signal (see, for example, description of FIG. 31):padding 3206 _(m), scrambler 3208 _(m), FEC 3210 _(m), interleaver 3212_(m), constellation mapping 3214 _(m), STBC 3216 _(m), and CSD 3218_(m), to generate k channels. Any of these elements may be omitted, forexample, STBC 3216 _(m). The k channels may be provided to frequencysegment mapper 3220 that may map the M layers to K frequency segments orchannels, and then IDFT 3222 _(1 . . . K) and GI removal 3224_(1 . . . K) may be applied to each of the k channels.

In the example of FIG. 32, one layer is mapped to one frequency segment.In another example, multiple layers may be mapped to one frequencysegment or one layer may be mapped to multiple frequency segments. TheIFFT/IDFT size utilized at STA side may be N_(FFT) as defined inEquation 9.

FIG. 33 shows an example transmission flow diagram 3300 at the AP side,where the AP may act as the receiver for UL communication. MU-PCA may besetup at the MAC layer; while in the PHY layer one or more packets maybe expected to arrive simultaneously at the assigned frequency segmentsx₁ . . . x_(k). For each segment x_(1 . . . k), following GI removal3302 _(1 . . . k) and inverse discrete Fourier transform (IDFTa) 3304_(1 . . . k), frequency segment de-mapping 3306 may map the data signalin frequency domain to multiple layers 3308 _(1 . . . m). Each layer3308 _(1 . . . m) may apply single-channel receiver processing to thedata of the corresponding layer, the processing which may include any ofthe following: MIMO detection 3310 _(1 . . . m), de-modulation 3312_(1 . . . m), de-interleaver 3314 _(1 . . . m), de-scrambler 3318_(1 . . . m), and padding removal 3320 _(1 . . . m). Layer de-mapper3322 may map the output of the layers 3308 _(1 . . . m) to MAC packets.This scheme may be applied with or without a MIMO scheme (i.e. MIMOdetection 3310 _(1 . . . m)). MIMO schemes may include, but are notlimited to, spatial multiplexing, space-time block codes, andbeamforming, for example.

MCS levels may be indicated in SIG field. A big SIG field may bedefined, which may include all the MCS levels used for a STA/user. Themapping between MCS levels and channels/resource blocks may be given inthe SIG field too. This “big” SIG field may be transmitted or repeatedover all the channels for the STA/user. In another example, the SIGfields may be divided into a common SIG field and individual SIG fields.The common SIG field may contain common information for thetransmission, and may be transmitted over the entire bandwidth/channelsfor a STA/user. The individual SIG field may contain the information forone frequency channel/band, for example, the MCS and length field forthe channel/band. The individual SIG field may be transmitted on itsassigned channel/band.

Other examples of PHY designs and procedures for MU PCA usingtransmit/receive with asymmetrical bandwidth are described. The STA mayneed to know the frequency allocation information. Each user may utilizeits own Fourier transform, or several users may share a relativelywideband Fourier transform. In an example, for a user/STA with onechannel or multiple contiguously aggregated channels, the IFFT/FFT sizemay be defined by the channel bandwidth allocated to this user/STA. Inan example, a STA/user may be assigned two contiguously aggregated 1 MHzchannels, and then the IFFT/FFT size may be 64. In another example, fora 1 MHz channel, the IFFT/FFT size utilized may be 32. In anotherexample, for a user with more than one non-contiguously aggregatedchannels, separate Fourier transforms or one Fourier transform may beused.

More than one user may share contiguously aggregated channels. In anexample, assume channel 1 may be separated (i.e. non contiguous) fromchannels 2, 3, and 4, which are contiguous. Assume that channel 1 may beallocated to user 1; channels 2 and 3 may be allocated to user 2, andchannel 4 may be allocated to user 3. In an example, separate Fouriertransforms may be used for different users. In the example above, user 2may utilize Fourier transform that covers channel 2 and channel 3; whileuser 3 may utilize a Fourier transform that covers channel 4. In anotherexample, one wideband Fourier transform may be used for contiguouschannels. For example, n the example above, STAs/users 2 and 3 mayutilize one wideband Fourier transform.

In another example, separate Fourier transforms may be utilized forseparate STAs/users. In this case, each STA/user may conduct its owntransmission function blocks. After constructing the OFDM signal in thetime domain, the signal may be shifted to its assigned frequencysegment. The frequency shift may be performed either at baseband or inthe RF domain. If the frequency shift is conducted in the RF domain, theprocessing of the signal may be the same as for MU PCA withtransmit/receive with symmetric bandwidth described above.

FIG. 34 shows an example transmission flow diagram 3400 at the AP sidefor DL transmission. Following layer mapping 3402, each layer 3404_(1 . . . M) may apply any of the following to the signal: padding 3406_(1 . . . M), scrambler 3408 _(1 . . . M), FEC 3410 _(1 . . . M),interleaver 3412 _(1 . . . M), constellation mapping 3414 _(1 . . . M),STBC 3416 _(1 . . . M), and CSD 3418 _(1 . . . M). Any of these elementsmay be omitted, for example, STBC 3416 _(1 . . . M).

In the example of FIG. 34, within each layer 3401 _(1 . . . M), spatialmapping 3420 _(1 . . . M) may generate a separate signal for each user,and a transmission flow may be applied to each user's signal, which mayinclude IDFT 4322 _(1 . . . M), and GI insertion 3424 _(1 . . . M).Then, within each layer 3404 _(1 . . . M), frequency shifter 3426_(1 . . . M) may shift the time domain signal to the k assignedfrequency segments/channels. The frequency shift may be performed eitherat baseband or in the RF domain. For each transmit antenna, thesummation 3428 of the time domain signals of all the users may betransmitted. The STF and LTF may be transmitted using the same bandwidthas data.

For a DL receiver design, the STA may need to know the frequency segmentassigned to it, and may use a single-channel receiver on that frequencysegment. For UL transmitter design, the STA may need to know thefrequency segment assigned to it, and may use a transmitter on thatfrequency segment. In an example for UL receiver design, at the AP side,the received signal may be down-converted into K streams, anddetection/decoding may be performed. In another example, the wholesignal may be down converted to baseband with the following centerfrequency:

$\begin{matrix}\frac{\left( {\left\lfloor {F_{C,{MAX}} + {{BW}\left( F_{C,{MAX}} \right)}} \right\rfloor - \left\lfloor {F_{C,{MIN}} + {{BW}\left( F_{C,{MIN}} \right)}} \right\rfloor} \right)}{2} & {{Equation}\mspace{14mu} 10}\end{matrix}$where F_(C,MAX)=max(F_(C,k)), F_(C,MIN)=min(F_(C,k)), and F_(C,k) is thecenter frequency of the k^(th) user. Narrow band filtering may beapplied on each frequency band, and followed by other receivingprocedures. This scheme may be applied with or without MIMO schemes.MIMO scheme include, but are not limited to, spatial multiplexing,space-time block codes, and beamforming, among others.

In the above, the PPDUs may be transmitted within the contention freeperiod, for example, when the MAC mechanism has set up the NAVprotection for the whole period, and other STAs may not need tounderstand the particular SIG fields in the PPDUs. If a non-MU-PCA STAmay need to detect a SIG field of the MU-PCA PPDUs, the PLCP header maybe modified, or other modifications may be made. For example, the MU-PCASTF and LTF transmission may be removed or reduced, and LSTF and LLTFmay be re-used. Like for symmetric transmit/receive, equal MCS andunequal MCS may be supported in this scheme. MCS levels may be indicatedin SIG field.

Due to the operation channel bandwidth limitation, one user may beassigned multiple MAC packets. Also, several users may share the sameMAC packet (e.g., broadcast packet or multicast packet). The PHY layermay be able to process all kinds of MAC packets for different scenarios.A general transmission block flow may be applied to asymmetricalbandwidth. A single user may be considered a special case for MU-PCAtransmissions. In this case, for a single user transmission, the layermapping may map one or more MAC packets to one layer. Then, one set ofcoding/modulation and MIMO scheme may be applied to this layer. Inanother example, layer mapping may map one or more MAC packets tomultiple layers. In another example, separate coding/modulation, andMIMO scheme may be applied to multiple layers.

Although the solutions described herein consider 802.11 specificprotocols, it is understood that the solutions described herein are notrestricted to this scenario and are applicable to other wireless systemsas well.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

What is claimed is:
 1. A wireless transmit/receive unit (WTRU) thatbelongs to a multi-user parallel channel access (MU-PCA) group of aplurality of WTRUs, the MU-PCA group of the plurality of WTRUs isconfigured to communicate via a plurality of channels managed by anaccess point (AP), the WTRU comprising: a receiver configured toreceive, from the access point (AP), over a channel of the plurality ofchannels that is associated with the WTRU, a group request-to-send(G-RTS) message inthcating that the AP is ready to transmit data,wherein the G-RTS is provided by the AP simultaneously over theplurality of channels to each of the plurality of WTRUs in the MU-PCAgroup; a transmitter configured to transmit a first clear-to-send (CTS)message, to the AP, over the channel associated with the WTRU,indicating that the WTRU is ready to receive on the channel associatedwith the WTRU; the receiver configured to receive a data message, fromthe AP, over the channel associated with the WTRU; and the transmitterconfigured to transmit at least one frame, to the AP, over the channelassociated with the WTRU, wherein the at least one frame includes anindication of uplink (UL) data that is one bit in length, and whereinthe indication is set to a predetermined bit value on a conthtion thatthe WTRU has uplink (UL) data to transmit to the AP.
 2. The WTRU ofclaim 1 wherein: on a conthtion that the indication is set to thepredetermined bit: the receiver is further configured to receive, fromthe AP, a second CTS message over the channel associated with the WTRU;and the transmitter, in response to the receiver receiving the secondCTS message, is further configured to transmit the uplink (UL) data, tothe AP, over the channel associated with the WTRU.
 3. The WTRU of claim1, wherein: the transmitter is configured to transmit the first CTSmessage while others of the plurality of WTRUs transmit other CTSmessages over remaining channels of the plurality of channels.
 4. TheWTRU of claim 1, wherein: the at least one frame is an acknowledgement(ACK) message, and the transmitter is configured to transmit the ACKmessage while others of the plurality of WTRUs transmit other ACKmessages.
 5. The WTRU of claim 1, wherein the at least one frame is anacknowledgement (ACK) message, and the first CTS message is a group CTS(G-CTS) message and the ACK message is a group ACK (G-ACK) message.
 6. Amethod for use in a wireless transmit/receive unit (WTRU) that belongsto a multi-user parallel channel access (MU-PCA) group of a plurality ofWTRUs, the MU-PCA group of the plurality of WTRUs is configured tocommunicate via a plurality of channels managed by an access point (AP),the method comprising: receiving, from the access point (AP), over achannel of the plurality of channels that is associated with the WTRU, agroup request-to-send (G-RTS) message indicating that the AP is ready totransmit data, wherein the G-RTS is provided by the AP simultaneouslyover the plurality of channels to each of the plurality of WTRUs in theMU-PCA; transmitting a first clear-to-send (CTS) message, to the AP,over the channel associated with the WTRU, indicating that the WTRU isready to receive on the channel associated with the WTRU; receiving adata message, from the AP, over the channel associated with the WTRU;and transmitting at least one frame, to the AP, over the channelassociated with the WTRU, wherein the at least one frame includes anindication of uplink (UL) data that is one bit in length, and whereinthe indication is set to a predetermined bit value on a condition thatthe WTRU has uplink (UL) data to transmit to the AP.
 7. The method ofclaim 6 further comprising: on a condition that the indication is set tothe predetermined bit value: receiving, from the AP, a second CTSmessage over the channel associated with the WTRU; and transmitting, inresponse to receiving the second CTS message, the uplink (UL) data, tothe AP, over the channel associated with the WTRU.
 8. The method ofclaim 6, wherein the transmitting the first CTS message includestransmitting the first CTS message while others of the plurality ofWTRUs transmit other CTS messages over remaining channels of theplurality of channels.
 9. The method of claim 6, wherein the at leastone frame is an acknowledgement (ACK) message, and the transmitting theACK message includes transmitting the ACK message while others of theplurality of WTRUs transmit other ACK messages.
 10. The method of claim6, wherein the at least one frame is an acknowledgement (ACK) message,and the first CTS message is a group CTS (G-CTS) message and the ACKmessage is a group ACK (G-ACK) message.
 11. An access point (AP) thatbelongs to a multi-user parallel channel access (MU-PCA) group of aplurality of wireless transmit/receive units (WTRUs) and is configuredto manage a plurality of channels within the MU-PCA group, the APcomprising: a transmitter configured to transmit, to a WTRU, over achannel associated with the WTRU, a group request-to-send (G-RTS)message indicating that the AP is ready to transmit data, whereintransmitter simultaneously transmits the G-RTS over the plurality ofchannels to each of the plurality of WTRUs in the MU-PCA group; areceiver configured to receive a first clear-to-send (CTS) message, fromthe WTRU, over the channel associated with the WTRU, indicating that theWTRU is ready to receive on the channel associated with the WTRU; thetransmitter configured to transmit data messages, to the WTRU, over thechannel associated with the WTRU; and the receiver configured to receiveat least one frame, from the WTRU, over the channel associated with theWTRU, wherein the at least one frame includes an indication of uplink(UL) data that is one bit in length, and wherein the indication is setto a predetermined bit value on a condition that the WTRU has uplink(UL) data to transmit to the AP.
 12. The AP of claim 11 furthercomprising: on a condition that the indication is set to thepredetermined bit value: the transmitter is further configured totransmit, to the WTRU, a second CTS message over the channel associatedwith the WTRU; and the receiver, in response to transmitting the secondCTS message, is further configured to receive the uplink (UL) data, fromthe WTRU, over the channel associated with the WTRU.
 13. The WTRU ofclaim 1, wherein the indication is included in a medium access control(MAC) header.
 14. The WTRU of claim 1, wherein the UL data includes atleast one of: a medium access control (MAC) protocol data unit (MPDU), aMAC service data unit (A-MSDU), an aggregated-MPDU (A-MPDU) and anaggregated MSDU (A-MSDU).
 15. The WTRU of claim 1, wherein the G-RTSmessage indicates that the AP is ready to transmit a plurality of datamessages to the plurality of WTRUs over the plurality of channelssimultaneously.
 16. The method of claim 6, wherein the indication isincluded in a medium access control (MAC) header.
 17. The method ofclaim 6, wherein the UL data includes at least one of: a methum accesscontrol (MAC) protocol data unit (MPDU), a MAC service data unit(A-MSDU), an aggregated-MPDU (A-MPDU) and an aggregated MSDU (A-MSDU).18. The method of claim 6, wherein the G-RTS message indicates that theAP is ready to transmit a plurality of data messages to the plurality ofWTRUs over the plurality of channels simultaneously.
 19. The AP of claim11, wherein the indication is included in a medium access control (MAC)header.
 20. The AP of claim 11, wherein the UL data includes at leastone of: a medium access control (MAC) protocol data unit (MPDU), a MACservice data unit (A-MSDU), an aggregated-MPDU (A-MPDU) and anaggregated MSDU (A-MSDU).
 21. The AP of claim 11, wherein the G-RTSmessage indicates that the AP is ready to transmit a plurality of datamessages to the plurality of WTRUs over the plurality of channelssimultaneously.
 22. The WTRU of claim 1 wherein: the transmitter isconfigured to transmit the at least one frame in response to thereceiver correctly receiving the data message from the AP.
 23. The WTRUof claim 1 wherein: the transmitter is configured to transmit the atleast one frame after the plurality of WTRUs receive data messages fromthe AP.
 24. The WTRU of claim 1 wherein: the receiver is configured toreceive the data message over the channel associated with the WTRU whileothers of the plurality of WTRUs receive other data messages overremaining channels of the plurality of channels.
 25. The method of claim6, wherein transmitting the at least one frame occurs in response toreceiving the data message from the AP.
 26. The method of claim 6,wherein transmitting the at least one frame occurs after the pluralityof WTRUs receive data messages from the AP.
 27. The method of claim 6,wherein receiving the data message includes receiving the data messageover the channel associated with the WTRU while others of the pluralityof WTRUs receive other data messages over remaining channels of theplurality of channels.
 28. The AP of claim 11, wherein: the receiver isconfigured to receive the at least one frame in response to thetransmitter transmitting the data message to the WTRU.
 29. The AP ofclaim 11, wherein: the receiver is configured to receive the at leastone frame in response to the transmitter transmitting data messages tothe plurality of WTRUs.
 30. The AP of claim 11, wherein: the receiver isconfigured to receive the first CTS message while receiving other CTSmessages from others of the plurality of WTRUs over remaining channelsof the plurality of channels.
 31. The AP of claim 11, wherein: the atleast one frame is an acknowledgement (ACK) message, and the receiver isconfigured to receive the ACK message while receiving other ACK messagesfrom others of the plurality of WTRUs.
 32. The AP of claim 11, wherein:the transmitter is configured to transmit the data message over thechannel associated with the WTRU while transmitting other data messagesto others of the plurality of WTRUs over remaining channels of theplurality of channels.